Quarterly report pursuant to Section 13 or 15(d)

Basis of presentation (Details)

v3.8.0.1
Basis of presentation (Details)
$ in Thousands
3 Months Ended 6 Months Ended 9 Months Ended
Feb. 20, 2015
contract
Sep. 30, 2017
USD ($)
segment
Jul. 14, 2016
segment
Sep. 30, 2017
USD ($)
segment
Sep. 30, 2016
USD ($)
Dec. 31, 2016
USD ($)
Interim Consolidated Financial Information            
Number of operating segments | segment   2 1 2    
Deferred income taxes   $ 59,027   $ 59,027   $ 54,563
Derivative Number of Contracts | contract 3          
Litigation proceeds       1,275 $ 10,050  
Accounting Standards Update 2015-17 [Member]            
Interim Consolidated Financial Information            
Deferred income taxes   $ 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%