Income Taxes - Reconciliation of Unrecognized Tax Benefits (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Beginning balance	$ 681	$ 506	$ 208
Additions based on tax positions of the current year	718	197	152
Additions based on tax positions of prior year	373	79	146
Additions resulting from acquisitions	277	0	0
Decreases due to lapse of applicable statute of limitations	(76)	0	0
Decreases related to settlements of prior year tax positions	0	(101)	0
Ending balance	$ 1,973	$ 681	$ 506