Common and Preferred Stock (Details) - USD ($) $ / shares in Units, $ in Thousands		1 Months Ended	3 Months Ended
	Dec. 01, 2015	Apr. 30, 2017	Mar. 31, 2018	Mar. 31, 2017	Dec. 31, 2017
Equity [Abstract]
Increase in share repurchase authorized amount	$ 300,000
Purchase of common stock (in shares)				82,000
Purchase of common shares at cost				$ 7,600
Purchase of common stock		$ 600	$ 0	$ 7,005
Remaining authorized repurchase amount			$ 550,900
Common stock, authorized (in shares)			150,000,000		150,000,000
Common stock, par value (in dollars per share)			$ 0.01		$ 0.01
Preferred stock, authorized (in shares)			5,000,000		5,000,000
Preferred stock, par value (in dollars per share)			$ 0.01		$ 0.01
Preferred stock, shares outstanding (in shares)			0		0