Condensed Consolidated Statements of Stockholders' Equity (Unaudited) (USD $) In Thousands, except Share data, unless otherwise specified	Total	Common Stock	Additional Paid-in Capital	Accumulated Other Comprehensive Income	Retained Earnings	Treasury Stock
Begining balances at Dec. 31, 2011	$ 1,284,519	$ 573	$ 637,605	$ 11,942	$ 1,059,624	$ (425,225)
Begining balances, Shares at Dec. 31, 2011		46,878,474				11,201,634
Changes in Stockholders' Equity [Roll Forward]
Common stock issued upon exercise of stock options, vesting of restricted stock grants and purchases under the employee stock purchase plan, Shares		604,738
Common stock issued upon exercise of stock options, vesting of restricted stock grants and purchases under the employee stock purchase plan	12,492	4	12,488
Common stock issued upon conversion of the 2.0% Convertible Senior Notes, Shares		2,127,399
Common stock issued upon conversion of the 2.0% Convertible Senior Notes	129,431	21	129,410
Common stock received through hedge instruments upon conversion of the 2.0% Convertible Senior Notes, Shares		(2,127,399)				2,127,399
Common stock received through hedge instruments upon conversion of the 2.0% Convertible Senior Notes	(129,431)					(129,431)
Compensation expense related to share-based payments	13,685		13,685
Tax benefit related to share-based payments	4,628		4,628
Employee stock relinquished for payment of taxes, Shares		(69,334)				69,334
Employee stock relinquished for payment of taxes	(4,337)					(4,337)
Unrealized gain on available-for-sale securities, net of tax	2,004			2,004
Net income	65,110				65,110
Ending balances at Jun. 30, 2012	$ 1,378,101	$ 598	$ 797,816	$ 13,946	$ 1,124,734	$ (558,993)
Ending balances, Shares at Jun. 30, 2012		47,413,878				13,398,367