Consolidated Statements Of Stockholders' Equity (USD $) In Thousands, except Share data	Common Stock [Member]	Additional Paid-In Capital [Member]	Retained Earnings [Member]	Accumulated Other Comprehensive Income/(Loss) [Member]	Total
Balance at Dec. 31, 2010	$ 1,179	$ 407,713	$ 336,363	$ (710)	$ 744,545
Balance, Shares at Dec. 31, 2010	117,904,975
Net income			94,072		94,072
Other comprehensive income (loss)				(2,790)	(2,790)
Issuance of common stock under employee plans, including tax benefits	27	32,878			32,905
Issuance of common stock under employee plans, including tax benefits, shares	2,715,253
Stock-based compensation		23,106			23,106
Business acquisition	1	1,813			1,814
Business acquisition, shares	56,915
Dividends paid			(47,961)		(47,961)
Disqualified dispositions		6,320			6,320
Balance at Dec. 31, 2011	1,207	471,830	382,474	(3,500)	852,011
Balance, Shares at Dec. 31, 2011	120,677,143
Net income			90,137		90,137
Other comprehensive income (loss)				4,344	4,344
Issuance of common stock under employee plans, including tax benefits	22	30,879			30,901
Issuance of common stock under employee plans, including tax benefits, shares	2,201,547
Stock-based compensation		27,679			27,679
Dividends paid			(68,401)		(68,401)
Disqualified dispositions		2,457			2,457
Balance at Dec. 31, 2012	1,229	532,845	404,210	844	939,128
Balance, Shares at Dec. 31, 2012	122,878,690				122,878,690
Net income			80,513		80,513
Other comprehensive income (loss)				1,706	1,706
Issuance of common stock under employee plans, including tax benefits	28	39,291			39,319
Issuance of common stock under employee plans, including tax benefits, shares	2,811,550
Stock-based compensation		29,151			29,151
Dividends paid			(69,776)		(69,776)
Disqualified dispositions		3,043			3,043
Balance at Dec. 31, 2013	$ 1,257	$ 604,330	$ 414,947	$ 2,550	$ 1,023,084
Balance, Shares at Dec. 31, 2013	125,690,240				125,690,240