Loans Receivable and Allowance for Credit Losses (Schedule of Allowance for Loan Losses by Portfolio Segment) (Detail) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Allowance for Loan and Lease Losses [Roll Forward]
Balance at beginning of period	$ 86,259	$ 62,810	$ 55,525	$ 55,562
Increase (decrease) due to the initial adoption of CECL - Retained earnings			7,920
Initial allowance on credit loans related to PCD loans	13,586		13,586
Provision charged to operations	6,411	500	32,011	10,200
Recoveries of loans previously charged-off	858	493	2,110	1,248
Loans charged-off	(800)	(6,459)	(4,838)	(9,666)
Balance at end of period	106,314	57,344	106,314	57,344
Mortgage Portfolio Segment
Allowance for Loan and Lease Losses [Roll Forward]
Balance at beginning of period	54,871	27,280	25,511	27,678
Increase (decrease) due to the initial adoption of CECL - Retained earnings			14,188
Initial allowance on credit loans related to PCD loans	11,984		11,984
Provision charged to operations	2,922	(2,092)	17,987	(2,814)
Recoveries of loans previously charged-off	35	24	143	361
Loans charged-off	(22)	(131)	(23)	(144)
Balance at end of period	69,790	25,081	69,790	25,081
Commercial Loans
Allowance for Loan and Lease Losses [Roll Forward]
Balance at beginning of period	25,284	33,549	28,263	25,693
Increase (decrease) due to the initial adoption of CECL - Retained earnings			(9,974)
Initial allowance on credit loans related to PCD loans	1,582		1,582
Provision charged to operations	2,767	2,880	12,672	13,337
Recoveries of loans previously charged-off	679	126	1,597	291
Loans charged-off	(727)	(6,212)	(4,555)	(8,978)
Balance at end of period	29,585	30,343	29,585	30,343
Consumer Loans
Allowance for Loan and Lease Losses [Roll Forward]
Balance at beginning of period	6,104	1,981	1,751	2,191
Increase (decrease) due to the initial adoption of CECL - Retained earnings			3,706
Initial allowance on credit loans related to PCD loans	20		20
Provision charged to operations	722	(288)	1,352	(323)
Recoveries of loans previously charged-off	144	343	370	596
Loans charged-off	(51)	(116)	(260)	(544)
Balance at end of period	$ 6,939	$ 1,920	$ 6,939	$ 1,920