Equity - Rollforward (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Equity activity
Balance at beginning of period			$ 758,648
Net income	$ 68,936	$ 25,377	89,295	$ 46,890
Stock-based compensation expense			2,897
Performance-based stock units			(8)
Stock option exercise			123
Non-controlling interests contribution			1,081
Common stock dividends			(45,168)
Other			(1,172)
Balance at end of period	$ 805,696		$ 805,696