Consolidated Statements of Changes in Stockholders' Equity (Parenthetical) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Tax expense (benefit) related to the delivery of Class A common stock in connection with share-base incentive compensation	$ 5,271	$ (448)	$ (13,138)
Tax expense (benefit) on delivery of Class A common stock in connection with business acquisitions	$ 28	$ (1,074)
Common stock, shares issued	129,766,091	129,766,091
Class A Common Stock [Member]
Common stock, shares issued	129,766,091	129,766,091	129,766,091