Condensed Consolidated Statements of Stockholders' Equity - 6 months ended Jun. 30, 2018 - USD ($) $ in Thousands	Total	Common Stock	Treasury Stock	Additional Paid-In Capital	Retained Earnings	Accumulated Other Comprehensive Loss
Beginning Balance at Dec. 31, 2017	$ 1,396,506	$ 812	$ (25,456)	$ 1,147,084	$ 287,992	$ (13,926)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	48,938				48,938
Unrealized gain on derivatives	6					6
Foreign currency translation adjustment	(541)					(541)
Pension and post-retirement liability	4,798					4,798
Cash dividend declared ($0.0625 per share)	(9,757)				(9,757)
Equity-based compensation	13,185			13,185
Proceeds from options exercised	62		93	(31)
Shares withheld for employee taxes related to vested restricted stock and stock units	(4,194)	3	(4,194)	(3)
Repurchase of common stock	(90,499)		(90,499)
Ending Balance at Jun. 30, 2018	$ 1,358,504	$ 815	$ (120,056)	$ 1,160,235	$ 327,173	$ (9,663)