Available for Sale Debt Securities - Disclosure on Securities Available for Sale with Temporary Impairment (Detail) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Debt Securities, Available-for-sale [Line Items]
Less than 12 months, fair value	$ 138,283	$ 226,072
Less than 12 months, gross unrealized losses	(644)	(2,282)
12 months or longer, fair value	46,819	545,880
12 months or longer, gross unrealized losses	(504)	(13,977)
Total, fair value	185,102	771,952
Total, gross unrealized losses	(1,148)	(16,259)
Mortgage-backed securities
Debt Securities, Available-for-sale [Line Items]
Less than 12 months, fair value	136,270	218,175
Less than 12 months, gross unrealized losses	(629)	(2,173)
12 months or longer, fair value	46,819	545,880
12 months or longer, gross unrealized losses	(504)	(13,977)
Total, fair value	183,089	764,055
Total, gross unrealized losses	(1,133)	(16,150)
Corporate obligations
Debt Securities, Available-for-sale [Line Items]
Less than 12 months, fair value	2,013	7,897
Less than 12 months, gross unrealized losses	(15)	(109)
12 months or longer, fair value	0	0
12 months or longer, gross unrealized losses	0	0
Total, fair value	2,013	7,897
Total, gross unrealized losses	$ (15)	$ (109)