Quarterly report pursuant to Section 13 or 15(d)

Basis of presentation (Details)

v3.7.0.1
Basis of presentation (Details)
$ in Thousands
3 Months Ended 6 Months Ended
Feb. 20, 2015
contract
Jun. 30, 2017
USD ($)
Jun. 30, 2017
USD ($)
segment
Jul. 14, 2016
segment
Jun. 30, 2016
USD ($)
Mar. 31, 2017
USD ($)
Dec. 31, 2016
USD ($)
Interim Consolidated Financial Information              
Number of operating segments | segment     2 1      
Deferred income taxes   $ 57,609 $ 57,609       $ 54,563
Derivative Number of Contracts | contract 3            
Litigation proceeds   1,275 1,275   $ 10,050    
Accounting Standards Update 2015-17 [Member]              
Interim Consolidated Financial Information              
Deferred income taxes   $ 5,726 $ 5,726     $ 5,726 $ 5,726
Interest Rate Swap Effective 31 December 2015 through 29 March 2018              
Interim Consolidated Financial Information              
Fixed interest rate (as a percent)   6.105% 6.105%        
Interest Rate Swap Effective 31 December 2015 through 29 March 2018 | London Interbank Offered Rate (LIBOR)              
Interim Consolidated Financial Information              
Interest rate added to variable rate (as a percent)   4.25% 4.25%        
LIBOR floor (as a percent)   1.00% 1.00%        
Interest Rate Swap Effective 29 March 2018 through 31 March 2020              
Interim Consolidated Financial Information              
Fixed interest rate (as a percent)   6.916% 6.916%        
Interest Rate Swap Effective 29 March 2018 through 31 March 2020 | London Interbank Offered Rate (LIBOR)              
Interim Consolidated Financial Information              
Interest rate added to variable rate (as a percent)   4.25% 4.25%        
LIBOR floor (as a percent)   1.00% 1.00%        
Interest Rate Swap Effective 31 March 2020 through 30 June 2021              
Interim Consolidated Financial Information              
Fixed interest rate (as a percent)   7.168% 7.168%        
Interest Rate Swap Effective 31 March 2020 through 30 June 2021 | London Interbank Offered Rate (LIBOR)              
Interim Consolidated Financial Information              
Interest rate added to variable rate (as a percent)   4.25% 4.25%        
LIBOR floor (as a percent)   1.00% 1.00%