Stockholders' Equity (Details) - USD ($) $ / shares in Units, $ in Thousands				3 Months Ended		6 Months Ended
	Aug. 04, 2016	May 09, 2016	Feb. 25, 2016	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015
Stockholders' Equity
Dividend declared (in dollars per share)		$ 0.48	$ 0.48	$ 0.48	$ 0.48	$ 0.96	$ 0.96
Gross proceeds from issuance of common stock						$ 177	$ 326,296
Authorized amount of share repurchases				$ 500,000		$ 500,000
Common stock repurchased (in shares)						1,052,889
Cost of common stock repurchased						$ 19,723	8,829
Remaining capacity under repurchase program				$ 282,100		$ 282,100
Shares issued under ATM Agreement						0
Underwriting and offering costs							$ 892
Subsequent Events
Stockholders' Equity
Dividend declared (in dollars per share)	$ 0.48