Assets and Liabilities Measured at Fair Value on Non-Recurring Basis (Detail) - USD ($) $ in Thousands		Mar. 31, 2020	Dec. 31, 2019	Dec. 31, 2018
Financial Assets:
Cash and cash equivalents		$ 1,334,206	$ 741,870	$ 1,474,955
FHLB stock	[1]	663,870	647,562
Loans, net		42,129,515	41,746,517
Financial Liabilities:
Deposits		31,972,766	31,657,132
Borrowed funds		14,932,827	14,557,593
Financial Assets:
Cash and cash equivalents		1,334,206	741,870
FHLB stock	[1]	663,870	647,562
Loans, net		41,750,688	41,699,929
Financial Liabilities:
Deposits		32,073,417	31,713,945
Borrowed funds		15,605,636	14,882,776
Quoted Prices in Active Markets for Identical Assets (Level 1)
Financial Assets:
Cash and cash equivalents		1,334,206	741,870
FHLB stock	[1]	0	0
Loans, net		0	0
Financial Liabilities:
Deposits	[2]	17,830,554	17,442,274
Borrowed funds		0	0
Significant Other Observable Inputs (Level 2)
Financial Assets:
Cash and cash equivalents		0	0
FHLB stock	[1]	663,870	647,562
Loans, net		0	0
Financial Liabilities:
Deposits	[3]	14,242,863	14,271,671
Borrowed funds		15,605,636	14,882,776
Significant Unobservable Inputs (Level 3)
Financial Assets:
Cash and cash equivalents		0	0
FHLB stock	[1]	0	0
Loans, net		41,750,688	41,699,929
Financial Liabilities:
Deposits		0	0
Borrowed funds		$ 0	$ 0

[1] Carrying value and estimated fair value are at cost.

[2] Interest-bearing checking and money market accounts, savings accounts, and non-interest-bearing accounts.

[3] Certificates of deposit.