Equity - Rollforward of Redeemable Noncontrolling Interest (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Redeemable Noncontrolling Interest, Equity, Carrying Amount
Balance - beginning of period	$ 965
Distributions	(20,643)	$ (17,030)	$ (14,713)
Redemption value adjustment		561	(8,873)
Balance - end of period	965	965
Redeemable Noncontrolling Interest
Redeemable Noncontrolling Interest, Equity, Carrying Amount
Balance - beginning of period	965	14,944	6,071
Distributions	0	(13,418)	0
Redemption value adjustment	0	(561)	8,873
Balance - end of period	$ 965	$ 965	$ 14,944