Property and Equipment - Summary of Internally Developed Capitalized Software (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016
Gross Carrying Amount
Gross Carrying Amount, Beginning Balance	$ 40,449
Disposals	(318)	$ (3,400)
Depreciation expense		(17)
Gross Carrying Amount, Ending Balance	45,090	40,449
Accumulated Depreciation
Accumulated Depreciation, Beginning Balance	(29,591)
Disposals		1,000
Depreciation expense	(5,485)	(4,763)
Accumulated Depreciation, Ending Balance	(34,050)	(29,591)
Net Carrying Amount, Beginning Balance	10,611
Net Carrying Amount, Ending Balance	11,040	10,611
Software
Gross Carrying Amount
Gross Carrying Amount, Beginning Balance	15,015	10,441
Additions	3,588	5,179
Disposals		(605)
Depreciation expense	0
Gross Carrying Amount, Ending Balance	18,603	15,015
Accumulated Depreciation
Accumulated Depreciation, Beginning Balance	(7,931)	(5,888)
Disposals	0	434
Depreciation expense	(3,898)	(2,477)
Accumulated Depreciation, Ending Balance	(11,829)	(7,931)
Net Carrying Amount, Beginning Balance	7,084	4,553
Disposals		(171)
Net Carrying Amount, Ending Balance	$ 6,774	$ 7,084