Consolidated Statements of Stockholders' Equity - 6 months ended Jun. 30, 2018 - USD ($) $ in Thousands	Total	Common stock [Member]	Additional paid-in capital [Member]	Treasury stock [Member]	Accumulated other comprehensive loss [Member]	Retained earnings [Member]
Balance (in shares) at Dec. 31, 2017		58,551,761
Balance at Dec. 31, 2017	$ 336,289	$ 59	$ 351,042	$ (239,199)	$ (642)	$ 225,029
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	24,343					24,343
Payment of dividends	(11,653)					(11,653)
Exercise of stock options and stock appreciation rights and vesting of restricted stock units (in shares)		320,163
Exercise of stock options and stock appreciation rights and vesting of restricted stock units	11		11
Employee taxes paid for 260,132 withheld shares upon equity award settlement	(25,184)			(25,184)
Stock-based compensation	24,953		24,896			57
Restricted stock grants (in shares)		506,191
Restricted stock grants	0	$ 0
Restricted stock cancellations (in shares)		(76,906)
Other comprehensive loss	(536)				(536)
Reclassification upon early adoption of ASU 2018-02	(167)				167	(167)
Balance (in shares) at Jun. 30, 2018		59,301,209
Balance at Jun. 30, 2018	$ 348,223	$ 59	$ 375,949	$ (264,383)	$ (1,011)	$ 237,609