Significant Accounting Policies - Reclassification (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cost of sales	$ 167,979	$ 156,868	$ 316,979	$ 299,341
Selling, general and administrative expenses	33,537	34,083	65,060	67,415
Other income (expense)	$ 2,580	(852)	$ 473	(3,638)
Previously Reported
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cost of sales		157,483		300,839
Selling, general and administrative expenses		33,676		66,651
Other income (expense)		(644)		(2,904)
Accounting Standards Update 2017-07 | Adjustment
New Accounting Pronouncements or Change in Accounting Principle [Line Items]
Cost of sales		(615)		(1,498)
Selling, general and administrative expenses		407		764
Other income (expense)		$ (208)		$ (734)