Borrowings - Summary of Information Pertaining to Borrowings (Detail) - USD ($) $ in Thousands	Sep. 30, 2016	Dec. 31, 2015
Long Term And Short Term Debt [Line Items]
Short-term borrowings	$ 605,949	$ 418,086
Long-term borrowings	60,922	162,662
Total Borrowings	$ 666,871	$ 580,748
Short-term borrowings, Weighted Average Rate	0.56%	0.44%
Long-term borrowings, Weighted Average Rate	3.06%	1.39%
Total Borrowings, Weighted Average Rate	0.79%	0.71%
Securities Sold under Repurchase Agreements
Long Term And Short Term Debt [Line Items]
Short-term borrowings	$ 40,949	$ 62,086
Short-term borrowings, Weighted Average Rate	0.01%	0.01%
Short-Term Borrowings
Long Term And Short Term Debt [Line Items]
Short-term borrowings	$ 565,000	$ 356,000
Short-term borrowings, Weighted Average Rate	0.60%	0.52%
Other Long-Term Borrowings
Long Term And Short Term Debt [Line Items]
Long-term borrowings	$ 15,303	$ 117,043
Long-term borrowings, Weighted Average Rate	2.91%	0.81%
Junior Subordinated Debt Securities
Long Term And Short Term Debt [Line Items]
Long-term borrowings	$ 45,619	$ 45,619
Long-term borrowings, Weighted Average Rate	3.11%	2.89%