Repurchases of Common Stock (Stock Repurchase Program - 2015) (Details) - USD ($)	12 Months Ended			36 Months Ended
	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 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
Repurchases of common stock	(159,800,000)	$ (545,140,000)	$ (195,004,000)	$ (896,175,000)
Authorized repurchase - as of December 31, 2015	$ 256,407,000	$ 163,655,000		$ 256,407,000