Loans Receivable, Net - Additional Information (Detail)		3 Months Ended		9 Months Ended		12 Months Ended
	May 02, 2016 USD ($)	Sep. 30, 2018 USD ($) SecurityLoan	Sep. 30, 2017 USD ($)	Sep. 30, 2018 USD ($) SecurityLoan	Sep. 30, 2017 USD ($)	Dec. 31, 2017 USD ($)
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans with non-accrual of interest		$ 19,239,000		$ 19,239,000		$ 20,865,000
Number of residential mortgage loans | SecurityLoan		0		0
Impaired loans on non-accrual commercial real estate, multi-family, land, construction, commercial and industrial loans				$ 250,000
Impaired loan portfolio total		$ 33,088,000		33,088,000		46,988,000
Allocation in allowance for loan losses		0		0		0
Average balance of impaired loans		32,900,000	$ 43,100,000	39,200,000	$ 38,000,000
Troubled debt restructured loans		27,800,000		27,800,000		42,100,000
Troubled debt restructured loans with accrual interest		24,200,000		24,200,000		33,300,000
Non-accrual loan total troubled debt restructurings				3,568,000		8,800,000
Specific reserves to loans accruing troubled debt restructurings		0		0
Sun Bancorp, Inc.
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		6,390,000		6,390,000		$ 4,190,000
Recorded investment in mortgage and consumer loans collateralized, foreclosure amount		2,100,000		2,100,000
Foreclosed property held		$ 447,000		$ 447,000