Quarterly report pursuant to Section 13 or 15(d)

Employee Stock Plans (Details)

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Employee Stock Plans (Details) (USD $)
In Thousands, except Share data, unless otherwise specified
 3 Months Ended 12 Months Ended
Mar. 31, 2013
Dec. 31, 2012
A&R 2004 Plan
    
Stock-based compensation    
Number of shares of common stock reserved for issuance 37,240  
Expiration period 10 years  
Recognized and unrecognized compensation expense with weighted average recognition period    
Number of awards permitted to be issued (in shares) 0  
2010 Plan
    
Stock-based compensation    
Maximum number of shares of common stock that may be issued 2,130,000  
Stock Options | A&R 2004 Plan
    
Options    
Balance at the end of the period (in per share) 37,240 37,240
Restricted Stock Share Awards
    
Shares    
Unvested at the beginning of the period (in shares) 208,823  
Granted (in shares) 44,022  
Vested (in shares) (41,325)  
Unvested at the end of the period (in shares) 211,520 208,823
Expected to vest in the future, at the end of the period (in shares) 203,905  
Weighted Average Grant Date Fair Value    
Unvested at the beginning of the period (in dollars per share) $ 12.63  
Granted (in dollars per share) $ 14.78  
Vested (in dollars per share) $ 14.64  
Unvested at the end of the period (in dollars per share) $ 12.68 $ 12.63
Expected to vest in the future, at the end of the period (in dollars per share) $ 12.68  
Weighted Average Remaining Contractual Term    
Unvested at the beginning of the period 2 years 29 days 1 year 11 months 8 days
Granted 2 years 9 months  
Unvested at the end of the period 2 years 29 days 1 year 11 months 8 days
Expected to vest in future, at the end of the period 2 years 29 days  
Recognized and unrecognized compensation expense with weighted average recognition period    
Compensation expenses recognized $ 286  
Unrecognized compensation expense, net of expected forfeitures, calculated under the fair value method for shares expected to vest 2,012  
Weighted average period over which unrecognized compensation expense is expected to be recognized 2 years 29 days  
Performance Share Unit Awards
    
Weighted Average Grant Date Fair Value    
Granted (in dollars per share) $ 14.40  
Recognized and unrecognized compensation expense with weighted average recognition period    
Vesting period of awards 2 years  
Compensation expenses recognized 16  
Unrecognized compensation expense, net of expected forfeitures, calculated under the fair value method for shares expected to vest 898  
Restricted Stock Unit Awards
    
Shares    
Unvested at the beginning of the period (in shares) 26,046  
Granted (in shares) 69,736  
Vested (in shares) (53,022)  
Unvested at the end of the period (in shares) 42,760 26,046
Expected to vest in the future, at the end of the period (in shares) 41,721  
Weighted Average Grant Date Fair Value    
Unvested at the beginning of the period (in dollars per share) $ 14.73  
Granted (in dollars per share) $ 14.52  
Vested (in dollars per share) $ 14.68  
Unvested at the end of the period (in dollars per share) $ 14.46 $ 14.73
Expected to vest in the future, at the end of the period (in dollars per share) $ 14.46  
Weighted Average Remaining Contractual Term    
Unvested at the beginning of the period 2 years 5 months 8 days 8 months 19 days
Granted 1 year 11 months 26 days  
Unvested at the end of the period 2 years 5 months 8 days 8 months 19 days
Expected to vest in future, at the end of the period 2 years 5 months 8 days  
Recognized and unrecognized compensation expense with weighted average recognition period    
Compensation expenses recognized 639  
Unrecognized compensation expense, net of expected forfeitures, calculated under the fair value method for shares expected to vest 561  
Accelerated stock based compensation expense $ 261  
Maximum period following a termination of service in which the share-based award will be settled 2 months 15 days  
Restricted Stock Unit Awards | Non-employee director
    
Recognized and unrecognized compensation expense with weighted average recognition period    
Number of shares issued upon exercise of units other than options 1  
Restricted Stock Unit Awards | Management
    
Recognized and unrecognized compensation expense with weighted average recognition period    
Minimum age of employee, attaining which awards are continued to be vested upon retirement 65  
Minimum service period, upon serving which awards are continued to be vested upon retirement 10 years  
Minimum age of employee along with service period condition, attaining which awards are continued to be vested upon retirement 55  
Number of shares issued upon exercise of units other than options 1