Condensed Consolidated Statement Of Stockholders' Equity - 6 months ended Jun. 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	94,560			94,560
Issuance of 226,187 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	9,762		9,762
Other comprehensive loss					(789)
Cash dividends ($1.15 per share)	(28,985)			(28,985)
Dividend equivalents on stock-based awards			670	(670)
Ending balance at Jun. 30, 2018	$ 713,179	$ 279	$ 200,306	$ 540,411	$ 1,650	$ (29,467)