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, 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
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
Net income			126,333		126,333
Other comprehensive income (loss)				(14,214)	(14,214)
Issuance of common stock under employee plans, including tax benefits	21	31,254			31,275
Issuance of common stock under employee plans, including tax benefits, shares	2,159,031
Stock-based compensation		26,242			26,242
Dividends paid			(76,287)		(76,287)
Disqualified dispositions		1,063			1,063
Balance at Dec. 31, 2014	$ 1,278	$ 662,889	$ 464,993	$ (11,664)	$ 1,117,496
Balance, Shares at Dec. 31, 2014	127,849,271				127,849,271