Repurchases of Common Stock (Details) - USD ($)	3 Months Ended	9 Months Ended
	Sep. 30, 2015	Sep. 30, 2015	Feb. 03, 2015
Summary Of Authorized Stock Repurchases [Roll Forward]
Authorized repurchase - as of January 1, 2015		$ 163,655,000
Additional board authorization			$ 250,000,000
Proceeds from the exercise of stock options		2,552,000
Repurchase of common stock from open market	$ (60,758,000)	(123,489,000)
Authorized repurchase - as of September 30, 2015	$ 292,718,000	$ 292,718,000