Summary of Significant Accounting Policies - Additional Information (Detail) - shares	1 Months Ended	12 Months Ended
	Dec. 31, 2002	Dec. 31, 2015
Property, Plant and Equipment [Line Items]
Cash and cash equivalents maturity period, days		90 days
Percentage of participants matched contribution		6.00%
Dividends paid on unallocated ESOP shares over period (in years)		30 years
Date of acquisition		Jul. 14, 2004
Shares held by the DDFP		372,817
Service period of employee subjected to elimination of postretirement healthcare benefits (in years)	10 years
Depositor Relationships [Member]
Property, Plant and Equipment [Line Items]
Amortized accelerated basis period (in years)		8 years 9 months 18 days
Building [Member] | Minimum [Member]
Property, Plant and Equipment [Line Items]
Estimated useful life, (in years)		25 years
Building [Member] | Maximum [Member]
Property, Plant and Equipment [Line Items]
Estimated useful life, (in years)		40 years
Furniture And Equipment [Member] | Minimum [Member]
Property, Plant and Equipment [Line Items]
Estimated useful life, (in years)		3 years
Furniture And Equipment [Member] | Maximum [Member]
Property, Plant and Equipment [Line Items]
Estimated useful life, (in years)		5 years
Beacon Trust [Member] | Customer Relationships [Member]
Property, Plant and Equipment [Line Items]
Amortized accelerated basis period (in years)		12 years
The MDE Group [Member] | Customer Relationships [Member]
Property, Plant and Equipment [Line Items]
Amortized accelerated basis period (in years)		10 years 4 months 24 days