Income Taxes - Tax Contingencies Reconciled (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Unrecognized tax benefits, as of January 1	$ 2,230	$ 1,265
Unrecognized tax benefits assumed in acquisition	0	513
Gross increases (decreases) – tax positions in current period	444	479
Gross increases (decreases) – prior year tax positions	58	0
Gross increases (decreases) – lapse of statute	(454)	(27)
Total benefit	$ 2,278	$ 2,230