Property and Equipment, Net - Additional Information (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Property Plant And Equipment [Abstract]
Depreciation expense	$ 1,968	$ 1,673	$ 1,348
Accumulated computer software capitalized	5,576	4,742
Computer software amortization	$ 1,226	$ 731