Revenue (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017	Jan. 02, 2018	Dec. 31, 2017
Revenue Initial Application Period Cumulative Effect Transition [Line Items]
Revenue	$ 233,080	$ 248,884	$ 655,087	$ 673,813
Cost of product sold	208,504	205,631	597,448	571,600
Net income (loss)	$ 12,691	$ 2,577	$ (24,919)	$ (24,478)
Income (loss) per common share
Basic	$ 0.17	$ 0.03	$ (0.33)	$ (0.34)
Diluted	$ 0.16	$ 0.03	$ (0.33)	$ (0.34)
Accounts receivable	$ 62,266		$ 62,266			$ 50,075
Inventories, net	69,474		69,474			72,904
Retained earnings	322,248		322,248			347,046
Accounting Standards Update 2014-09 [Member]
Income (loss) per common share
Accounts receivable					$ 50,856
Inventories, net					72,244
Retained earnings					$ 347,167
Balances without the adoption of ASC 606 | Accounting Standards Update 2014-09 [Member]
Revenue Initial Application Period Cumulative Effect Transition [Line Items]
Revenue	233,322		655,606
Cost of product sold	208,675		597,929
Net income (loss)	$ 12,762		$ (24,881)
Income (loss) per common share
Basic	$ 0.17		$ (0.33)
Diluted	$ 0.17		$ (0.33)
Accounts receivable	$ 62,004		$ 62,004
Inventories, net	69,652		69,652
Retained earnings	322,319		322,319
Effect of Change Higher/(Lower) | Accounting Standards Update 2014-09 [Member]
Revenue Initial Application Period Cumulative Effect Transition [Line Items]
Revenue	(242)		(519)
Cost of product sold	(171)		(481)
Net income (loss)	$ (71)		$ (38)
Income (loss) per common share
Basic	$ 0		$ 0
Diluted	$ (0.01)		$ 0
Accounts receivable	$ 262		$ 262			781
Inventories, net	(178)		(178)			(660)
Retained earnings	$ (71)		$ (71)			$ 121