Derivative Instruments - Summary of Gross Fair Values of Individual Derivative Instruments (Detail) - USD ($) $ in Thousands	Jun. 30, 2019	Dec. 31, 2018
Derivatives, Fair Value [Line Items]
Net Amounts of Assets Presented in the Consolidated Balance Sheet, Derivative Assets	$ 72,376	$ 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	88,245	76,699
Derivative Liability, Fair Value, Amount Not Offset Against Collateral	86,427
Gross Amount of Collateral Received/Pledged Not Offset in the Consolidated Balance Sheet, Derivative Liabilities		70,505
Net Amount, Derivative Assets	72,376	59,468
Derivative Asset, Fair Value, Gross Asset	72,615	59,768
Derivative Asset, Fair Value, Amount Offset Against Collateral	239	300
Derivative liabilities	88,484	76,999
Derivative Liability, Fair Value, Amount Offset Against Collateral	239	300
Derivative Liabilities Net Amount	1,818	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	62,941	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	1,818,273	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	62,941	66,302
Derivative Asset, Fair Value, Gross Asset	62,941	66,302
Derivative Asset, Fair Value, Amount Offset Against Collateral	0	0
Derivative liabilities	1,818,273	1,712,062
Derivative Liability, Fair Value, Amount Offset Against Collateral	0	0
Derivative Liabilities Net Amount	1,818,273	1,712,062
Interest Rate Swap [Member]
Derivatives, Fair Value [Line Items]
Net Amounts of Assets Presented in the Consolidated Balance Sheet, Derivative Assets	72,156	59,468
Derivative Asset, Fair Value, Amount Not Offset Against Collateral		0
Net Amounts of Liabilities Presented in the Consolidated Balance Sheet, Derivative Liabilities	87,384	71,861
Derivative Liability, Fair Value, Amount Not Offset Against Collateral	86,427	67,126
Net Amount, Derivative Assets	72,156	59,468
Derivative Asset, Fair Value, Gross Asset	72,395	59,768
Derivative Asset, Fair Value, Amount Offset Against Collateral	239	300
Derivative liabilities	87,623	72,161
Derivative Liability, Fair Value, Amount Offset Against Collateral	239	300
Derivative Liabilities Net Amount	957	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	1,818,273	1,712,062
Derivative liabilities	1,818,273	1,712,062
Derivative Liabilities Net Amount	1,818,273	1,712,062
Future [Member]
Derivatives, Fair Value [Line Items]
Net Amounts of Assets Presented in the Consolidated Balance Sheet, Derivative Assets	220
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	220
Derivative Asset, Fair Value, Gross Asset	220
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	861	1,459
Derivative liabilities	861	1,459
Derivative Liability, Fair Value, Amount Offset Against Collateral	0	0
Derivative Liabilities Net Amount	861	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	62,941	66,302
Derivative Asset, Fair Value, Amount Not Offset Against Collateral		0
Net Amount, Derivative Assets	62,941	66,302
Derivative Asset, Fair Value, Gross Asset	62,941	$ 66,302
Derivative Asset, Fair Value, Amount Offset Against Collateral	$ 0