Offsetting Assets and Liabilities - Offsetting of Derivative Liabilities (Detail) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Derivatives:
Gross amounts of recognized liabilities, derivatives	$ 352	$ 10,239
Gross amounts offset in the consolidated balance sheet, derivatives	0	0
Net amounts of liabilities presented in the consolidated balance sheet, derivatives	352	10,239
Financial instruments, derivatives	0	(2,058)
Collateral received, derivatives	(320)	(7,836)
Net amount, derivatives	32	345
Repurchase Agreements:
Gross amounts of recognized liabilities, repurchase agreements	17,532,303	13,602,484
Gross amounts offset in the consolidated balance sheet, repurchase agreements	0	0
Net amounts of assets presented in the consolidated balance sheet, repurchase agreements	17,532,303	13,602,484
Financial instruments, repurchase agreements	(17,532,303)	(13,602,484)
Collateral received, repurchase agreements	0	0
Net amount, repurchase agreements	0	0
Secured Loans:
Gross amounts of recognized liabilities, secured loans	1,650,000	1,650,000
Gross amounts offset in the consolidated balance sheet, secured loans	0	0
Net amounts of assets presented in the consolidated balance sheet, secured loans	1,650,000	1,650,000
Financial instruments, secured loans	(1,650,000)	(1,650,000)
Collateral received, secured loans	0	0
Net amount, secured loans	0	0
Total gross amount of recognized liabilities	19,182,655	15,262,723
Total gross amounts offset in the consolidated balance sheets	0	0
Net amounts of assets presented in the consolidated balance sheets	19,182,655	15,262,723
Total financial instruments	(19,182,303)	(15,254,542)
Total collateral received	(320)	(7,836)
Total net amount	32	345
Fair value of securities pledged against derivatives	189,780	159,914
Cash collateral received	170	18,083
Cash collateral pledged on derivatives	116,400	13,500
Securities sold under agreements to repurchase fair value of collateral	19,122,295	15,047,528
Collateral pledged against secured loans	1,900,000	1,900,000
Centrally Cleared Interest Rate Swaps
Secured Loans:
Fair value of securities pledged against derivatives	189,800	158,300
Interest Rate Swaps
Secured Loans:
Cash collateral received	160	18,083
Repurchase Agreements
Secured Loans:
Cash collateral received	10	0
Cash
Secured Loans:
Securities sold under agreements to repurchase fair value of collateral	$ 32,568	$ 0