Balance Sheet Offsetting - Financial Instruments Eligible for Offset Consolidated Balance Sheet (Detail) - USD ($) $ in Thousands	Jun. 30, 2018	Dec. 31, 2017
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Gross Amount Recognized, Derivatives, Financial Assets	$ 8,068	$ 3,810
Gross Amount Offset, Derivatives, Financial assets	0	0
Net Amount Recognized, Derivatives, Financial assets	8,068	3,810
Gross Amount Recognized, Resell agreements, Financial assets	9,642	9,642
Gross Amount Offset, Resell agreements, Financial assets	0	0
Net Amount Recognized, Resell agreements, Financial assets	9,642	9,642
Gross Amount Recognized, Financial assets	17,710	13,452
Gross Amount Offset, Financial assets	0	0
Net Amount Recognized, Financial assets	17,710	13,452
Gross Amount Recognized, Derivatives, Financial Liabilities	38,345	27,375
Gross Amount Offset, Derivatives, Financial liabilities	0	0
Net Amount Recognized, Derivatives, Financial liabilities	38,345	27,375
Gross Amount Recognized, Repurchase agreements, Financial liabilities	968,420	1,117,199
Gross Amount Offset, Repurchase agreements, Financial liabilities	0	0
Net Amount Recognized, Repurchase agreements, Financial liabilities	968,420	1,117,199
Gross Amount Recognized, Financial liabilities	1,006,765	1,144,574
Gross Amount Offset, Financial liabilities	0	0
Net Amount Recognized, Financial Liabilities	1,006,765	1,144,574
Loan/lease interest rate swaps and caps [Member]
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Gross Amount Recognized, Derivatives, Financial Assets	5,993	2,140
Gross Amount Offset, Derivatives, Financial assets	0	0
Net Amount Recognized, Derivatives, Financial assets	5,993	2,140
Commodity swaps and options [Member]
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Gross Amount Recognized, Derivatives, Financial Assets	2,068	1,592
Gross Amount Offset, Derivatives, Financial assets	0	0
Net Amount Recognized, Derivatives, Financial assets	2,068	1,592
Gross Amount Recognized, Derivatives, Financial Liabilities	31,575	13,774
Gross Amount Offset, Derivatives, Financial liabilities	0	0
Net Amount Recognized, Derivatives, Financial liabilities	31,575	13,774
Foreign currency forward contracts [Member]
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Gross Amount Recognized, Derivatives, Financial Assets	7	78
Gross Amount Offset, Derivatives, Financial assets	0	0
Net Amount Recognized, Derivatives, Financial assets	7	78
Gross Amount Recognized, Derivatives, Financial Liabilities	216	188
Gross Amount Offset, Derivatives, Financial liabilities	0	0
Net Amount Recognized, Derivatives, Financial liabilities	216	188
Loan/lease interest rate swaps [Member]
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Gross Amount Recognized, Derivatives, Financial Liabilities	6,554	13,413
Gross Amount Offset, Derivatives, Financial liabilities	0	0
Net Amount Recognized, Derivatives, Financial liabilities	$ 6,554	$ 13,413