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, 2018	Dec. 31, 2017	Dec. 31, 2016
Stockholders' Equity Attributable to Noncontrolling Interest [Roll Forward]
Balance at January 1,	$ 39,206	$ 44,684	$ 45,452
Reclassifications due to change in redemption value and other	1,164	65	(768)
Redemptions	(4,895)	(5,543)	0
Balance at December 31,	$ 35,475	$ 39,206	$ 44,684