Loans Receivable, Net - Additional Information (Detail)		3 Months Ended		9 Months Ended		12 Months Ended
	Jan. 31, 2019 USD ($)	Sep. 30, 2019 USD ($) SecurityLoan	Sep. 30, 2018 USD ($)	Sep. 30, 2019 USD ($) SecurityLoan	Sep. 30, 2018 USD ($)	Dec. 31, 2018 USD ($)
Accounts, Notes, Loans and Financing Receivable [Line Items]
Impaired loans on non-accrual commercial real estate, multi-family, land, construction, commercial and industrial loans				$ 250,000
Impaired loan portfolio total		$ 27,817,000		27,817,000		$ 29,797,000
Allocation in allowance for loan losses		547,000		547,000		0
Average balance of impaired loans		28,200,000	$ 32,900,000	30,200,000	$ 39,200,000
Troubled debt restructured loans		25,100,000		25,100,000		26,500,000
Loans with non-accrual of interest		$ 17,453,000		$ 17,453,000		17,415,000
Number of residential mortgage loans | SecurityLoan		0		0
Non-accrual loan total troubled debt restructurings				$ 6,200,000		3,600,000
Specific reserves to loans accruing troubled debt restructurings		$ 547,000		547,000		0
Troubled debt restructured loans with accrual interest		19,000,000.0		19,000,000.0		22,900,000
Capital Bank
Accounts, Notes, Loans and Financing Receivable [Line Items]
Allowance for loan and lease losses, loans acquired	$ 0
Residential Real Estate
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans with non-accrual of interest		5,953,000		5,953,000		$ 7,389,000
Recorded investment in mortgage and consumer loans collateralized, foreclosure amount		2,100,000		2,100,000
Foreclosed property held		$ 81,000		$ 81,000