Stockholders' Equity (Details) - USD ($) $ / shares in Units, $ in Thousands		3 Months Ended
	May. 09, 2016	Mar. 31, 2016	Mar. 31, 2015
Stockholders' Equity
Dividend declared (in dollars per share)		$ 0.48	$ 0.48
Gross proceeds from issuance of common stock		$ 82	$ 55
Authorized amount of share repurchases		$ 500,000
Common stock repurchased (in shares)		1,052,889
Cost of common stock repurchased		$ 19,723
Remaining capacity under repurchase program		$ 282,100
Shares issued under ATM Agreement		0
Subsequent event
Stockholders' Equity
Dividend declared (in dollars per share)	$ 0.48