Loans Receivable and Allowance for Credit Losses on Loans (Summary of Allowance for Loan Losses by Portfolio Segment and Impairment Classification) (Detail) - USD ($) $ in Thousands	Mar. 31, 2020	Jan. 01, 2020	Dec. 31, 2019	Mar. 31, 2019	Dec. 31, 2018
Financing Receivable, Allowance for Credit Losses [Line Items]
Individually evaluated for impairment	$ 5,699		$ 5,067
Collectively evaluated for impairment	69,444		50,458
Total gross loans	75,143	$ 55,525	55,525	$ 55,353	$ 55,562
Mortgage Portfolio Segment
Financing Receivable, Allowance for Credit Losses [Line Items]
Individually evaluated for impairment	1,590		1,580
Collectively evaluated for impairment	45,910		23,931
Total gross loans	47,500		25,511	26,926	27,678
Commercial Loans
Financing Receivable, Allowance for Credit Losses [Line Items]
Individually evaluated for impairment	4,073		3,462
Collectively evaluated for impairment	18,768		24,801
Total gross loans	22,841	28,228	28,263	26,351	25,693
Consumer Loans
Financing Receivable, Allowance for Credit Losses [Line Items]
Individually evaluated for impairment	36		25
Collectively evaluated for impairment	4,766		1,726
Total gross loans	$ 4,802	$ 1,746	$ 1,751	$ 2,076	$ 2,191