Loans Receivable, Net - Additional Information (Detail) - USD ($)		12 Months Ended
	Jul. 31, 2015	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans pledged		$ 2,918,000,000
Impaired loans on non-accrual commercial real estate, multi-family, land, construction, commercial and industrial loans		250,000
Impaired loan portfolio total		29,800,000	$ 47,000,000
Specific reserves to loans accruing troubled debt restructurings		0	0	$ 510,000
Average balance of impaired loans		38,100,000	39,800,000	38,400,000
Interest income on non-accrual loans		419,000	639,000	391,000
Troubled debt restructuring loans		26,500,000	42,100,000
Troubled debt restructuring loans with accrual interest		22,900,000	33,300,000	27,000,000
Commitments to lend additional funds to borrowers		0
Loans with non-accrual of interest		17,415,000	20,865,000	13,600,000
Financing receivables 90 days past due and still accruing		0
Non-accrual loan total troubled debt restructurings		3,600,000	8,800,000	$ 3,500,000
Allowance for loan losses		0
Colonial American Bank
Accounts, Notes, Loans and Financing Receivable [Line Items]
Allowance for loan losses	$ 0
Residential mortgage
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans with non-accrual of interest		7,389,000	$ 4,190,000
Recorded investment in mortgage and consumer loans collateralized, foreclosure amount		2,200,000
Foreclosed property held		$ 700,000