Office Closing and Termination Costs - Exit Costs Included in Accrued Liabilities in Consolidated Balance Sheet (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Exit costs included in accrued liabilities in consolidated balance sheet
Beginning balance at December 31, 2017			$ 1,855
Accrued severance costs	$ (356)	$ 0	(356)	$ 2,422
Accrued building rent			(17)
Payments			(1,417)
Ending balance at September 30, 2018	$ 65		$ 65