Stockholders' Equity (Details) - USD ($)		3 Months Ended
	Feb. 23, 2017	Mar. 31, 2017	Mar. 31, 2016	Feb. 28, 2017
Stockholders' Equity
Dividend declared (in dollars per share)	$ 0.48	$ 0.48	$ 0.48
Shares issued under ATM Agreement		0	0
Authorized amount of share repurchases				$ 500,000,000
Common stock repurchased (in shares)		0	1,052,889
Cost of common stock repurchased			$ 19,723,000
Remaining capacity under repurchase program		$ 262,200,000
Convertible Senior Notes
Stockholders' Equity
Face amount of debt repurchased			0
Debt repurchased amount			$ 0