Equity - Rollforward (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Equity activity
Balance at beginning of period			$ 740,048
Net income	$ 20,616	$ 22,411	67,506	$ 64,449
Proceeds from common stock issued, net of issuance costs			14,529
Stock-based compensation expense			3,967
Performance-based stock units			(6)
Stock option exercise			202
Common stock dividends			(67,664)
Other			(1,947)
Balance at end of period	$ 756,635		$ 756,635