Loans Receivable and Allowance for Loan Losses - Allowance for Loan Losses by Portfolio Segment (Detail) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Allowance for Loan and Lease Losses [Roll Forward]
Balance at beginning of period				$ 55,562				$ 60,195	$ 55,562	$ 60,195	$ 61,883
Provision charged to operations	$ 2,900	$ 500	$ 9,500	200	$ 1,800	$ 1,000	$ 15,500	5,400	13,100	23,700	5,600
Recoveries of loans previously charged off									1,895	1,685	1,653
Loans charged off									(15,032)	(30,018)	(8,941)
Balance at end of period	55,525				55,562				55,525	55,562	60,195
Mortgage Portfolio Segment
Allowance for Loan and Lease Losses [Roll Forward]
Balance at beginning of period				27,678				28,052	27,678	28,052
Provision charged to operations									(2,323)	(586)
Recoveries of loans previously charged off									422	489
Loans charged off									(266)	(277)
Balance at end of period	25,511				27,678				25,511	27,678	28,052
Commercial Portfolio Segment
Allowance for Loan and Lease Losses [Roll Forward]
Balance at beginning of period				25,693				29,814	25,693	29,814
Provision charged to operations									15,928	24,437
Recoveries of loans previously charged off									665	428
Loans charged off									(14,023)	(28,986)
Balance at end of period	28,263				25,693				28,263	25,693	29,814
Consumer Portfolio Segment
Allowance for Loan and Lease Losses [Roll Forward]
Balance at beginning of period				$ 2,191				$ 2,329	2,191	2,329
Provision charged to operations									(505)	(151)
Recoveries of loans previously charged off									808	768
Loans charged off									(743)	(755)
Balance at end of period	$ 1,751				$ 2,191				$ 1,751	$ 2,191	$ 2,329