Office Closing and Exit Costs - Exit Costs Included in Accrued Liabilities in Consolidated Balance Sheet (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Exit costs included in accrued liabilities in consolidated balance sheet
Beginning balance	$ 1,855	$ 2,460
Accrued severance costs	(356)	2,176	$ (822)
Accrued building rent	(17)	(70)
Payments	(1,482)	(2,711)
Ending balance	$ 0	$ 1,855	$ 2,460