Property and Equipment, Net - Summary of Property and Equipment, Net (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016
Property Plant and Equipment [Line Items]
Property and equipment at cost	$ 74,859	$ 61,432
Less: Accumulated depreciation	(26,120)	(17,627)
Property and equipment, net	48,739	43,805
Land
Property Plant and Equipment [Line Items]
Property and equipment at cost	972	543
Equipment
Property Plant and Equipment [Line Items]
Property and equipment at cost	12,171	10,094
Furniture, fixtures, and leasehold improvements
Property Plant and Equipment [Line Items]
Property and equipment at cost	21,280	15,415
Computer hardware, software, and phone equipment
Property Plant and Equipment [Line Items]
Property and equipment at cost	9,571	7,535
Buildings
Property Plant and Equipment [Line Items]
Property and equipment at cost	2,559	2,253
Deemed assets from landlord building construction
Property Plant and Equipment [Line Items]
Property and equipment at cost	22,752	22,752
Construction-in-Progress
Property Plant and Equipment [Line Items]
Property and equipment at cost	$ 5,554	$ 2,840