Balance Sheet Offsetting - Financial Instruments Eligible for Offset Consolidated Balance Sheet (Detail) - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Gross Amount Recognized, Derivative, Financial Assets	$ 27,849	$ 3,810
Gross Amount Offset, Derivatives, Financial Assets	0	0
Net Amount Recognized, Derivative, Financial Assets	27,849	3,810
Gross Amount Recognized, Resell Agreements, Financial Assets	11,642	9,642
Gross Amount Offset, Resell Agreements, Financial Assets	0	0
Net Amount Recognized, Resell Agreements, Financial Assets	11,642	9,642
Gross Amount Recognized, Financial Assets	39,491	13,452
Gross Amount Offset, Financial Assets	0	0
Net Amount Recognized, Financial Assets	39,491	13,452
Gross Amount Recognized, Derivative, Financial Liabilities	11,185	27,375
Gross Amount Offset, Derivative, Financial Liabilities	0	0
Net Amount Recognized, Derivative, Financial Liabilities	11,185	27,375
Gross Amount Recognized, Repurchase Agreements, Financial Liabilities	1,360,298	1,117,199
Gross Amount Offset, Repurchase Agreements, Financial Liabilities	0	0
Net Amount Recognized, Repurchase Agreements, Financial Liabilities	1,360,298	1,117,199
Gross Amount Recognized, Financial Liabilities	1,371,483	1,144,574
Gross Amount Offset, Financial Liabilities	0	0
Net Amount Recognized, Financial Liabilities	1,371,483	1,144,574
Loan Lease Interest Rate Swaps And Caps [Member]
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Gross Amount Recognized, Derivative, Financial Assets	3,100	2,140
Gross Amount Offset, Derivatives, Financial Assets	0	0
Net Amount Recognized, Derivative, Financial Assets	3,100	2,140
Commodity Swaps And Options [Member]
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Gross Amount Recognized, Derivative, Financial Assets	24,749	1,592
Gross Amount Offset, Derivatives, Financial Assets	0	0
Net Amount Recognized, Derivative, Financial Assets	24,749	1,592
Gross Amount Recognized, Derivative, Financial Liabilities	1,918	13,774
Gross Amount Offset, Derivative, Financial Liabilities	0	0
Net Amount Recognized, Derivative, Financial Liabilities	1,918	13,774
Foreign Currency Forward Contracts [Member]
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Gross Amount Recognized, Derivative, Financial Assets	0	78
Gross Amount Offset, Derivatives, Financial Assets	0	0
Net Amount Recognized, Derivative, Financial Assets	0	78
Gross Amount Recognized, Derivative, Financial Liabilities	147	188
Gross Amount Offset, Derivative, Financial Liabilities	0	0
Net Amount Recognized, Derivative, Financial Liabilities	147	188
Loan Lease Interest Rate Swaps [Member]
Fair Value, Off-balance Sheet Risks, Disclosure Information [Line Items]
Gross Amount Recognized, Derivative, Financial Liabilities	9,120	13,413
Gross Amount Offset, Derivative, Financial Liabilities	0	0
Net Amount Recognized, Derivative, Financial Liabilities	$ 9,120	$ 13,413

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