Balance Sheet Offsetting - Financial Instruments Eligible for Offset Consolidated Balance Sheet (Detail) - USD ($) $ in Thousands	Sep. 30, 2017	Dec. 31, 2016
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Gross Amount Recognized, Derivatives, Financial Assets	$ 3,457	$ 3,798
Gross Amount Offset, Derivatives, Financial assets	0	0
Net Amount Recognized, Derivatives, Financial assets	3,457	3,798
Gross Amount Recognized, Resell agreements, Financial assets	17,642	9,642
Gross Amount Offset, Resell agreements, Financial assets	0	0
Net Amount Recognized, Resell agreements, Financial assets	17,642	9,642
Gross Amount Recognized, Financial assets	21,099	13,440
Gross Amount Offset, Financial assets	0	0
Net Amount Recognized, Financial assets	21,099	13,440
Gross Amount Recognized, Derivatives, Financial Liabilities	16,883	32,534
Gross Amount Offset, Derivatives, Financial liabilities	0	0
Net Amount Recognized, Derivatives, Financial liabilities	16,883	32,534
Gross Amount Recognized, Repurchase agreements, Financial liabilities	987,869	963,317
Gross Amount Offset, Repurchase agreements, Financial liabilities	0	0
Net Amount Recognized, Repurchase agreements, Financial liabilities	987,869	963,317
Gross Amount Recognized, Financial liabilities	1,004,752	995,851
Gross Amount Offset, Financial liabilities	0	0
Net Amount Recognized, Financial Liabilities	1,004,752	995,851
Loan/lease interest rate swaps and caps [Member]
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Gross Amount Recognized, Derivatives, Financial Assets	1,590	3,592
Gross Amount Offset, Derivatives, Financial assets	0	0
Net Amount Recognized, Derivatives, Financial assets	1,590	3,592
Commodity swaps and options [Member]
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Gross Amount Recognized, Derivatives, Financial Assets	1,849	206
Gross Amount Offset, Derivatives, Financial assets	0	0
Net Amount Recognized, Derivatives, Financial assets	1,849	206
Gross Amount Recognized, Derivatives, Financial Liabilities	1,392	5,757
Gross Amount Offset, Derivatives, Financial liabilities	0	0
Net Amount Recognized, Derivatives, Financial liabilities	1,392	5,757
Foreign currency forward contracts [Member]
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Gross Amount Recognized, Derivatives, Financial Assets	18	0
Gross Amount Offset, Derivatives, Financial assets	0	0
Net Amount Recognized, Derivatives, Financial assets	18	0
Gross Amount Recognized, Derivatives, Financial Liabilities	104	33
Gross Amount Offset, Derivatives, Financial liabilities	0	0
Net Amount Recognized, Derivatives, Financial liabilities	104	33
Loan/lease interest rate swaps [Member]
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Gross Amount Recognized, Derivatives, Financial Liabilities	15,387	26,744
Gross Amount Offset, Derivatives, Financial liabilities	0	0
Net Amount Recognized, Derivatives, Financial liabilities	$ 15,387	$ 26,744