Condensed Consolidated Statement Of Stockholders' Equity - 9 months ended Sep. 30, 2018 - USD ($) $ in Thousands	Total	Common Stock	Paid-in Capital	Retained Earnings	Accumulated Other Comprehensive Income	Treasury Stock
Beginning balance at Dec. 31, 2017	$ 652,745	$ 277	$ 203,990	$ 475,506	$ 2,439	$ (29,467)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	128,372			128,372
Issuance of 228,146 shares of common stock pursuant to stock-based awards, net of shares tendered for payment of taxes	(14,114)	2	(14,116)
Stock-based compensation expense	13,852		13,852
Other comprehensive loss					(1,095)
Cash dividends ($1.75 per share)	(44,114)			(44,114)
Dividend equivalents on stock-based awards			1,022	(1,022)
Ending balance at Sep. 30, 2018	$ 735,646	$ 279	$ 204,748	$ 558,742	$ 1,344	$ (29,467)