Acquisition - Additional Information (Detail) - USD ($) $ in Thousands		3 Months Ended		9 Months Ended
	Apr. 04, 2017	Sep. 30, 2017	Sep. 30, 2016	Sep. 30, 2017	Sep. 30, 2016
Business Acquisition [Line Items]
Business acquisition, net revenue generated		$ 334,555	$ 65,281	$ 462,574	$ 188,223
Business acquisition, net loss generated		(157,208)	$ (5,415)	$ (163,321)	(13,402)
Headway
Business Acquisition [Line Items]
Ownership Interest acquired	100.00%
Business acquisition date				Apr. 04, 2017
Aggregate cash consideration	$ 7,500
Cash acquired	4,500
Fair value of contingent consideration	$ 18,000
Contingent consideration agreement, payment period	3 years
Contingent consideration arrangements, minimum	$ 0
Contingent consideration arrangements, maximum	31,500
Contingent consideration, payment	$ 2,000
Contingent payment for key employees remain with the Company, requisite service period	18 months
Accounts receivables assets acquired, fair value	$ 20,100
Gross amount account receivables asset acquired	21,200
Amount due under contract expected to be uncollectible	$ 1,100
Business acquisition, net revenue generated		12,700		$ 23,800
Business acquisition, net loss generated		$ 200		700
Acquisition fees and costs				$ 500	$ 0