Derivative Instruments - Summary of Gross Fair Values of Individual Derivative Instruments (Detail) - USD ($) $ in Thousands	Sep. 30, 2019	Dec. 31, 2018
Derivatives, Fair Value [Line Items]
Derivative, Collateral, Right to Reclaim Cash	$ 50,310	$ 102,904
Net Amounts of Assets Presented in the Consolidated Balance Sheet, Derivative Assets	82,162	59,468
Derivative Asset, Fair Value, Amount Not Offset Against Collateral	0	0
Net Amounts of Liabilities Presented in the Consolidated Balance Sheet, Derivative Liabilities	103,314	76,699
Derivative Liability, Fair Value, Amount Not Offset Against Collateral	102,076
Gross Amount of Collateral Received/Pledged Not Offset in the Consolidated Balance Sheet, Derivative Liabilities		70,505
Net Amount, Derivative Assets	82,162	59,468
Derivative Asset, Fair Value, Gross Asset	82,230	59,768
Derivative Asset, Fair Value, Amount Offset Against Collateral	68	300
Derivative liabilities	103,382	76,999
Derivative Liability, Fair Value, Amount Offset Against Collateral	68	300
Derivative Liabilities Net Amount	1,238	6,194
Variable Interest Entity, Primary Beneficiary [Member]
Derivatives, Fair Value [Line Items]
Net Amounts of Assets Presented in the Consolidated Balance Sheet, Derivative Assets	67,921	66,302
Derivative Asset, Fair Value, Amount Not Offset Against Collateral	0	0
Net Amounts of Liabilities Presented in the Consolidated Balance Sheet, Derivative Liabilities	1,779,077	1,712,062
Derivative Liability, Fair Value, Amount Not Offset Against Collateral	0
Gross Amount of Collateral Received/Pledged Not Offset in the Consolidated Balance Sheet, Derivative Liabilities		0
Net Amount, Derivative Assets	67,921	66,302
Derivative Asset, Fair Value, Gross Asset	67,921	66,302
Derivative Asset, Fair Value, Amount Offset Against Collateral	0	0
Derivative liabilities	1,779,077	1,712,062
Derivative Liability, Fair Value, Amount Offset Against Collateral	0	0
Derivative Liabilities Net Amount	1,779,077	1,712,062
Interest Rate Swap [Member]
Derivatives, Fair Value [Line Items]
Net Amounts of Assets Presented in the Consolidated Balance Sheet, Derivative Assets	81,769	59,468
Derivative Asset, Fair Value, Amount Not Offset Against Collateral		0
Net Amounts of Liabilities Presented in the Consolidated Balance Sheet, Derivative Liabilities	102,892	71,861
Derivative Liability, Fair Value, Amount Not Offset Against Collateral	102,076	67,126
Net Amount, Derivative Assets	81,769	59,468
Derivative Asset, Fair Value, Gross Asset	81,837	59,768
Derivative Asset, Fair Value, Amount Offset Against Collateral	68	300
Derivative liabilities	102,960	72,161
Derivative Liability, Fair Value, Amount Offset Against Collateral	68	300
Derivative Liabilities Net Amount	816	4,735
Interest Rate Swap [Member] | Variable Interest Entity, Primary Beneficiary [Member]
Derivatives, Fair Value [Line Items]
Net Amounts of Liabilities Presented in the Consolidated Balance Sheet, Derivative Liabilities	1,779,077	1,712,062
Derivative liabilities	1,779,077	1,712,062
Derivative Liabilities Net Amount	1,779,077	1,712,062
Future [Member]
Derivatives, Fair Value [Line Items]
Net Amounts of Assets Presented in the Consolidated Balance Sheet, Derivative Assets	393
Net Amounts of Liabilities Presented in the Consolidated Balance Sheet, Derivative Liabilities		3,379
Derivative Liability, Fair Value, Amount Not Offset Against Collateral		3,379
Net Amount, Derivative Assets	393
Derivative Asset, Fair Value, Gross Asset	393
Derivative Asset, Fair Value, Amount Offset Against Collateral	0
Derivative liabilities		3,379
Derivative Liability, Fair Value, Amount Offset Against Collateral		0
Derivative Liabilities Net Amount		0
Other Credit Derivatives [Member]
Derivatives, Fair Value [Line Items]
Net Amounts of Liabilities Presented in the Consolidated Balance Sheet, Derivative Liabilities	422	1,459
Derivative liabilities	422	1,459
Derivative Liability, Fair Value, Amount Offset Against Collateral	0	0
Derivative Liabilities Net Amount	422	1,459
Currency Swaps [Member] | Variable Interest Entity, Primary Beneficiary [Member]
Derivatives, Fair Value [Line Items]
Net Amounts of Assets Presented in the Consolidated Balance Sheet, Derivative Assets	67,921	66,302
Derivative Asset, Fair Value, Amount Not Offset Against Collateral		0
Net Amount, Derivative Assets	67,921	66,302
Derivative Asset, Fair Value, Gross Asset	67,921	$ 66,302
Derivative Asset, Fair Value, Amount Offset Against Collateral	$ 0