Consolidated Statement Of Stockholders' Equity - USD ($) $ in Thousands	Total	Common Stock	Paid-in Capital	Accumulated Other Comprehensive (Loss) Income	Retained Earnings	Treasury Stock
Beginning Balance at Dec. 31, 2014	$ 394,898	$ 265	$ 147,186		$ 276,914	$ (29,467)
Net income	74,345				74,345
Issuance of common stock pursuant to stock-based awards, net of shares tendered for payment of taxes	(7,558)	5	(7,563)
Income tax benefit relating to issuance of common stock pursuant to stock-based awards	9,028		9,028
Stock-based compensation expense	14,043		14,043
Issuance of deferred stock units relating to prior year compensation	2,046		2,046
Cash dividend	(48,227)				(48,227)
Dividend equivalents on stock-based awards			1,826		(1,826)
Ending Balance at Dec. 31, 2015	438,575	270	166,566		301,206	(29,467)
Net income	129,671				129,671
Issuance of common stock pursuant to stock-based awards, net of shares tendered for payment of taxes	(5,409)	4	(5,413)
Income tax benefit relating to issuance of common stock pursuant to stock-based awards	7,983		7,983
Stock-based compensation expense	15,420		15,420
Issuance of deferred stock units relating to prior year compensation	264		264
Other comprehensive income (loss)	(1,798)			$ (1,798)
Cash dividend	(34,437)				(34,437)
Dividend equivalents on stock-based awards			1,161		(1,161)
Ending Balance at Dec. 31, 2016	550,269	274	185,981	(1,798)	395,279	(29,467)
Net income	132,884				132,884
Issuance of common stock pursuant to stock-based awards, net of shares tendered for payment of taxes	(10,531)	3	(10,534)
Stock-based compensation expense	20,036		20,036
Issuance of deferred stock units relating to prior year compensation	6,907		6,907
Other comprehensive income (loss)				4,237
Cash dividend	(51,057)				(51,057)
Dividend equivalents on stock-based awards			1,600		(1,600)
Ending Balance at Dec. 31, 2017	$ 652,745	$ 277	$ 203,990	$ 2,439	$ 475,506	$ (29,467)