CONDENSED CONSOLIDATED STATEMENT OF STOCKHOLDERS' EQUITY (Unaudited) (USD $)	Total	Common Stock	Additional Paid-in Capital	Accumulated Other Comprehensive Income	Retained Earnings	Treasury Stock
Beginning Balance at Dec. 31, 2010	$ 1,165,637,000	$ 554,000	$ 543,611,000	$ 627,000	$ 864,003,000	$ (243,158,000)
Beginning Balance, Shares at Dec. 31, 2010		48,167,229				7,759,234
Common stock issued upon exercise of stock options, vesting of restricted stock grants and purchases under the employee stock purchase plan	40,020,000	13,000	40,007,000
Common stock issued upon exercise of stock options, vesting of restricted stock grants and purchases under the employee stock purchase plan, Shares		1,497,239
Compensation expense related to share-based payments	10,757,000		10,757,000
Tax benefit related to share-based payments	12,614,000		12,614,000
Employee stock relinquished for payment of taxes	(3,621,000)					(3,621,000)
Employee stock relinquished for payment of taxes, Shares		(55,040)				55,040
Common stock repurchases	(79,997,000)					(79,997,000)
Common stock repurchases, Shares	1,254,933	(1,254,933)				1,254,933
Unrealized gain on available-for-sale securities, net of tax	5,355,000			5,355,000
Net income	114,771,000				114,771,000
Ending Balance at Jun. 30, 2011	$ 1,265,536,000	$ 567,000	$ 606,989,000	$ 5,982,000	$ 978,774,000	$ (326,776,000)
Ending Balance, Shares at Jun. 30, 2011		48,354,495				9,069,207