Summary of Critical and Significant Accounting Policies Summary of Critical and Significant Accounting Policies - Redeemable Noncontrolling Interests (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Stockholders' Equity Attributable to Noncontrolling Interest [Roll Forward]
Balance at January 1,	$ 44,684	$ 45,452	$ 23,256
Reclassifications due to change in redemption value and other	65	(768)	22,196
Redemptions	(5,543)	0	0
Balance at December 31,	$ 39,206	$ 44,684	$ 45,452