Investment Securities - Additional Information on Securities in a Continuous Loss Position (Detail) $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2020 USD ($) Security	Dec. 31, 2019 USD ($) Security
Schedule of Available-for-sale Securities
Number of debt securities with unrealized losses | Security	13	123
Debt securities with unrealized losses (percentage of amortized cost)	0.82%	0.58%
Number of securities | Security	6,000	69,000
Amortized cost basis	$ 6,236	$ 294,631
Unrealized loss	$ 95	$ 2,382
Mortgage-backed securities: Residential agency
Schedule of Available-for-sale Securities
Number of securities | Security	2,000	59,000
Amortized cost basis	$ 1,980	$ 279,587
Unrealized loss	$ 7	$ 2,130
Mortgage-backed securities: Commercial agency
Schedule of Available-for-sale Securities
Number of securities | Security	0	6,000
Amortized cost basis	$ 0	$ 10,453
Unrealized loss	$ 0	$ 152
Other securities
Schedule of Available-for-sale Securities
Number of securities | Security	4,000	4,000
Amortized cost basis	$ 4,256	$ 4,591
Unrealized loss	$ 88	$ 100