Borrowings - Summary of Information Pertaining to Borrowings (Detail) - USD ($) $ in Thousands	Jun. 30, 2015	Dec. 31, 2014
Long Term And Short Term Debt [Line Items]
Short-term borrowings	$ 277,210	$ 320,605
Long-term borrowings	163,847	65,061
Total Borrowings	$ 441,057	$ 385,666
Short-term borrowings, Weighted Average Rate	0.28%	0.27%
Long-term borrowings, Weighted Average Rate	1.31%	2.79%
Total Borrowings, Weighted Average Rate	0.66%	0.70%
Securities Sold under Repurchase Agreements [Member]
Long Term And Short Term Debt [Line Items]
Short-term borrowings	$ 46,235	$ 30,605
Short-term borrowings, Weighted Average Rate	0.01%	0.01%
Short-Term Borrowings [Member]
Long Term And Short Term Debt [Line Items]
Short-term borrowings	$ 230,975	$ 290,000
Short-term borrowings, Weighted Average Rate	0.33%	0.31%
Other Long-Term Borrowings [Member]
Long Term And Short Term Debt [Line Items]
Long-term borrowings	$ 118,228	$ 19,442
Long-term borrowings, Weighted Average Rate	0.76%	3.00%
Junior Subordinated Debt Securities [Member]
Long Term And Short Term Debt [Line Items]
Long-term borrowings	$ 45,619	$ 45,619
Long-term borrowings, Weighted Average Rate	2.74%	2.70%