Equity - Rollforward (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Equity activity
Balance at beginning of period			$ 740,048
Net income	$ 25,377	$ 22,180	46,890	$ 42,038
Proceeds from common stock issued, net of issuance costs			14,529
Stock-based compensation expense			2,684
Performance-based stock units			(6)
Stock option exercise			79
Common stock dividends			(45,110)
Other			(1,947)
Balance at end of period	$ 757,167		$ 757,167