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	15,509	5	15,504
Common stock issued upon exercise of stock options, vesting of restricted stock grants and purchases under the employee stock purchase plan, Shares		701,456
Common stock issued upon conversion of the 2.0% Convertible Senior Notes	129,431	21	129,410
Common stock issued upon conversion of the 2.0% Convertible Senior Notes, Shares		2,127,399
Common stock received through hedge instruments upon conversion of the 2.0% Convertible Senior Notes	(129,431)					(129,431)
Reissuance of treasury stock for net share settlement of warrants	153,778		(153,778)			153,778
Reissuance of treasury stock for net share settlement of warrants, shares		1,694,232				(1,694,232)
Common stock received through hedge instruments upon conversion of the 2.0% Convertible Senior Notes, Shares		(2,127,399)				2,127,399
Compensation expense related to share-based payments	20,386		20,386
Tax benefit related to share-based payments, net	6,157		6,157
Employee stock relinquished for payment of taxes	(4,337)					(4,337)
Employee stock relinquished for payment of taxes, Shares		(69,334)				69,334
Unrealized gain on available-for-sale securities, net of tax	7,869			7,869
Net income	96,842				96,842
Ending balances at Sep. 30, 2012	$ 1,426,945	$ 599	$ 655,284	$ 19,811	$ 1,156,466	$ (405,215)
Ending balances, Shares at Sep. 30, 2012		49,204,828				11,704,135