Contingent Liabilities and Commitments - Additional Information (Detail) - USD ($) $ in Thousands	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Loss Contingencies [Line Items]
Contingent liability	$ 462,622	$ 495,395	$ 506,888	$ 520,375
Guarantee of indebtedness, relating to unused letters of credit	5,600
Escrow Account Deposit
Loss Contingencies [Line Items]
Contingent liability	1,300,000
Exchange Traded Funds
Loss Contingencies [Line Items]
Contingent liability	$ 1,000,000