Common Stock (Narrative) (Details) - USD ($) $ / shares in Units, $ in Thousands	1 Months Ended		12 Months Ended			24 Months Ended	36 Months Ended
	Mar. 31, 2016	May 31, 2014	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2015	Dec. 31, 2016
Equity [Abstract]
Common stock, shares outstanding (in shares)			30,856,841	30,410,467		30,410,467	30,856,841
Proceeds from issuance of common stock			$ 0	$ 230,600	$ 503,420	$ 754,600	$ 764,800
Proceeds from issuance of common stock, dividend reinvestment plan						$ 24,900	$ 46,000
Dividends declared per day (in dollars per share)	$ 0.004132513665	$ 0.0041438356
Dividends declared per common share (in usd per share)		$ 1.5125	$ 1.51	$ 1.51	$ 0.84