Short-Term Borrowings - Schedule of Short-Term Borrowings and Weighted-Average Interest Rates (Detail) (USD $) In Thousands, unless otherwise specified	6 Months Ended
	Jun. 30, 2014	Dec. 31, 2013	Jun. 30, 2013
Short-term Debt [Line Items]
Outstanding at end of period	$ 467,578	$ 462,332	$ 530,381
Average amount outstanding	390,170
Weighted average interest rate during period	0.08%
Weighted average interest rate at end of period	0.10%
Federal Funds Purchased [Member]
Short-term Debt [Line Items]
Outstanding at end of period	150,188
Average amount outstanding	80,393
Maximum amount outstanding at any month-end	182,847
Weighted average interest rate during period	0.17%
Weighted average interest rate at end of period	0.19%
Repurchase Agreements [Member]
Short-term Debt [Line Items]
Outstanding at end of period	317,390
Average amount outstanding	309,777
Maximum amount outstanding at any month-end	$ 317,390
Weighted average interest rate during period	0.05%
Weighted average interest rate at end of period	0.05%