Equity - Rollforward (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Mar. 31, 2016
Equity activity
Balance at beginning of period	$ 740,048
Net income	21,513	$ 19,858
Proceeds from common stock issued, net of issuance costs	14,529
Stock-based compensation expense	1,259
Performance-based stock units	(6)
Common stock dividends	(22,552)
Other	(1,651)
Balance at end of period	$ 753,140