Incentive Plans - Summary of Impact of Share-Based Incentive Plans on Compensation and Benefits Expense (Detail) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Share-based incentive awards:
Share-based incentive awards	$ 272,965	$ 261,462	$ 226,723
RSUs [Member]
Share-based incentive awards:
Share-based incentive awards	190,821	171,188	166,395
PRSUs [Member]
Share-based incentive awards:
Share-based incentive awards	40,767	43,018	36,529
Restricted Stock [Member]
Share-based incentive awards:
Share-based incentive awards	39,369	45,536	22,342
DSUs [Member]
Share-based incentive awards:
Share-based incentive awards	$ 2,008	$ 1,720	$ 1,457