Property and Equipment - Additional Information (Detail) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Property, Plant and Equipment [Line Items]
Depreciation and amortization expense	$ 18,517,000	$ 15,949,000	$ 10,600,000
Remaining unamortized capitalized internal use software costs	4,172,000	1,052,000
Software [Member]
Property, Plant and Equipment [Line Items]
Depreciation expense	$ 1,057,000	$ 213,000	$ 238,000