Loans Receivable, Net - Additional Information (Detail)		3 Months Ended		12 Months Ended
	May 02, 2016 USD ($)	Mar. 31, 2018 USD ($) SecurityLoan	Mar. 31, 2017 USD ($)	Dec. 31, 2017 USD ($)
Accounts, Notes, Loans and Financing Receivable [Line Items]
Loans with non-accrual of interest		$ 18,251,000		$ 20,865,000
Number of residential mortgage loans | SecurityLoan		0
Impaired loans on non-accrual commercial real estate, multi-family, land, construction, commercial and industrial loans		$ 250,000
Impaired loan portfolio total		44,060,000		46,988,000
Allocation in allowance for loan losses		1,605,000		0
Average balance of impaired loans		45,500,000	$ 33,200,000
Troubled debt restructured loans		38,100,000		42,100,000
Troubled debt restructured loans with accrual interest		33,800,000		33,300,000
Non-accrual loan total troubled debt restructurings		4,306,000		8,800,000
Specific reserves to loans accruing troubled debt restructurings		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		5,686,000		$ 4,190,000
Recorded investment in mortgage and consumer loans collateralized, foreclosure amount		1,200,000
Foreclosed property held		$ 941,000