Fair Value Measurement - Level 3 Liability (Details) $ in Thousands	3 Months Ended
	Mar. 31, 2018 USD ($)
Accounts payable and accrued expenses
Fair Value, Liabilities Measured On Recurring Basis, Unobservable Input Reconciliation [Line Items]
Short-term portion of deferred payments	$ 400
Deferred payments [Member]
Schedule of changes in fair value of level 3 liability
Balance at beginning of year	4,514
Amounts paid	(656)
Other adjustments to fair value	698
Balance at end of year	$ 4,556