Loans Receivable and Allowance for Credit Losses (Schedule of Allowance for Loan Losses by Portfolio Segment) (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2020	Jun. 30, 2019	Jun. 30, 2020	Jun. 30, 2019
Allowance for Loan and Lease Losses [Roll Forward]
Balance at beginning of period	$ 75,143	$ 55,353	$ 55,525	$ 55,562
Provision charged to operations	10,900	9,500	25,600	9,700
Recoveries of loans previously charged-off	724	342	1,252	755
Loans charged-off	(508)	(2,385)	(4,038)	(3,207)
Balance at end of period	86,259	62,810	86,259	62,810
Mortgage Portfolio Segment
Allowance for Loan and Lease Losses [Roll Forward]
Balance at beginning of period	47,500	26,926	25,511	27,678
Provision charged to operations	7,355	262	15,066	(720)
Recoveries of loans previously charged-off	16	105	108	336
Loans charged-off	0	(13)	(2)	(14)
Balance at end of period	54,871	27,280	54,871	27,280
Commercial Loans
Allowance for Loan and Lease Losses [Roll Forward]
Balance at beginning of period	22,841	26,351	28,263	25,693
Provision charged to operations	2,285	9,175	9,904	10,457
Recoveries of loans previously charged-off	605	113	918	165
Loans charged-off	(447)	(2,090)	(3,827)	(2,766)
Balance at end of period	25,284	33,549	25,284	33,549
Consumer Loans
Allowance for Loan and Lease Losses [Roll Forward]
Balance at beginning of period	4,802	2,076	1,751	2,191
Provision charged to operations	1,260	63	630	(37)
Recoveries of loans previously charged-off	103	124	226	254
Loans charged-off	(61)	(282)	(209)	(427)
Balance at end of period	$ 6,104	$ 1,981	$ 6,104	$ 1,981