Property and Equipment, net - Additional Information (Details) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Property, Plant and Equipment, Net [Abstract]
Property, Plant and Equipment, Disposals	$ 501,000	$ 207,000	$ 76,000
Depreciation expense	$ 5,919,000	$ 4,771,000	$ 3,510,000