Loans Receivable and Allowance for Loan Losses (Schedule of Allowance for Loan Losses by Portfolio Segment) (Detail) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016
Allowance for Loan and Lease Losses [Roll Forward]
Balance at beginning of period	$ 62,155	$ 62,191	$ 61,883	$ 61,424
Provision charged (credited) to operations	1,700	1,700	3,200	3,200
Recoveries of loans previously charged-off	305	813	993	1,393
Loans charged-off	(1,298)	(3,771)	(3,214)	(5,084)
Balance at end of period	62,862	60,933	62,862	60,933
Mortgage Loans [Member]
Allowance for Loan and Lease Losses [Roll Forward]
Balance at beginning of period	29,318	30,849	29,626	32,094
Provision charged (credited) to operations	(292)	497	(423)	(695)
Recoveries of loans previously charged-off	7	401	61	573
Loans charged-off	(207)	(113)	(438)	(338)
Balance at end of period	28,826	31,634	28,826	31,634
Commercial Loans [Member]
Allowance for Loan and Lease Losses [Roll Forward]
Balance at beginning of period	29,786	28,255	29,143	25,829
Provision charged (credited) to operations	1,777	1,311	3,394	4,269
Recoveries of loans previously charged-off	73	192	531	283
Loans charged-off	(551)	(3,459)	(1,983)	(4,082)
Balance at end of period	31,085	26,299	31,085	26,299
Consumer Loans [Member]
Allowance for Loan and Lease Losses [Roll Forward]
Balance at beginning of period	3,051	3,087	3,114	3,501
Provision charged (credited) to operations	215	(108)	229	(374)
Recoveries of loans previously charged-off	225	220	401	537
Loans charged-off	(540)	(199)	(793)	(664)
Balance at end of period	2,951	3,000	2,951	3,000
Total Portfolio Segments [Member]
Allowance for Loan and Lease Losses [Roll Forward]
Balance at beginning of period	62,155	62,191	61,883	61,424
Provision charged (credited) to operations	1,700	1,700	3,200	3,200
Recoveries of loans previously charged-off	305	813	993	1,393
Loans charged-off	(1,298)	(3,771)	(3,214)	(5,084)
Balance at end of period	62,862	60,933	62,862	60,933
Unallocated [Member]
Allowance for Loan and Lease Losses [Roll Forward]
Balance at beginning of period	0	0	0	0
Provision charged (credited) to operations	0	0	0	0
Recoveries of loans previously charged-off	0	0	0	0
Loans charged-off	0	0	0	0
Balance at end of period	$ 0	$ 0	$ 0	$ 0