Fair Value Measurements - Textual (Details) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Stock Authorized During Period, Value, To be Issued		$ 27,852,000
Stock Issued During Period, Shares, New Issues			0	0
Business Combination, Contingent Consideration, Liability	$ 83,695,000	122,426,000
Common Stock
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Redemption value adjustments	$ 0
Stock Issued During Period, Shares, New Issues			691,559
Common Class A
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Redemption value adjustments		3,353,939
Common Class A | Common Stock
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Redemption value adjustments		$ 28,727,000	$ 10,458,000