Other Non-Current Liabilities - Components of Other Non-Current Liabilities (Detail) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Other Liabilities Disclosure [Abstract]
Premise related costs	$ 18,735	$ 18,188
Accrued earnout payments	6,980	8,518
Other	1,658	1,582
Total other non-current liabilities	$ 27,373	$ 28,288