Fair Value Measurement - Level 3 Liability (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Schedule of changes in fair value of level 3 liability
Balance at beginning of year	$ 11,741	$ 3,278
Amounts paid	(1,133)	(7,358)
Contingent consideration in connection with NYCDA acquisition		14,500
Other adjustments to fair value	(6,094)	1,321
Balance at end of year	4,514	$ 11,741
Accounts payable and accrued expenses
Fair Value, Liabilities Measured On Recurring Basis, Unobservable Input Reconciliation [Line Items]
Short-term portion of deferred payments	$ 1,300