Equity - Rollforward (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2016	Mar. 31, 2015
Equity activity
Balance at beginning of period	$ 659,202
Net income	19,858	$ 17,552
Proceeds from common stock offering, net of offering costs	14,327
Vesting of stock option and restricted common stock	990
Reclassification adjustment	(28)	$ (9)
Common stock dividends	(20,347)
Other	(1,312)
Balance at end of period	$ 672,690