Condensed Consolidated Statement Of Stockholders' Equity - 3 months ended Mar. 31, 2017 - USD ($) $ in Thousands	Total	Common Stock	Paid-in Capital	Retained Earnings	Accumulated Other Comprehensive Loss	Treasury Stock
Beginning balance at Dec. 31, 2016	$ 550,269	$ 274	$ 185,981	$ 395,279	$ (1,798)	$ (29,467)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	43,145
Issuance of 155,641 shares of common stock pursuant to stock-based awards, net of shares tendered for payment of taxes	7,650	(2)	7,652
Stock-based compensation expense	3,902		3,902
Issuance of 63,677 deferred stock units relating to prior year compensation	6,907		6,907
Other comprehensive loss	349				349
Cash dividend ($0.50 per share)	(12,442)			(12,442)
Dividend equivalents on stock-based awards			398	(398)
Ending balance at Mar. 31, 2017	$ 584,480	$ 276	$ 189,536	$ 425,584	$ (1,449)	$ (29,467)