Fair Value of Assets and Liabilities - Additional information (Detail) - USD ($)	3 Months Ended								12 Months Ended
	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2016	Dec. 31, 2015
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Liabilities measured at fair value on recurring basis					$ 0					$ 0
Fair value, assets, level 1 to level 2 transfers, amount	$ 0				0				$ 0	0
Fair value, assets, level 2 to level 1 transfers, amount	0				0				0	0
Fair value, liabilities, level 1 to level 2 transfers, amount	0				0				0	0
Fair value, liabilities, level 2 to level 1 transfers, amount	0				0				0	0
Net gain on sales of mortgage loans	3,241,000	$ 5,401,000	$ 1,058,000	$ 681,000	622,000	$ 755,000	$ 608,000	$ 582,000	10,381,000	2,567,000
Liabilities measured at fair value on nonrecurring basis	0				$ 0				0	0
Increase in valuation allowance									390,000	$ 34,000
Residential Mortgage Loans [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Aggregate fair value of loans held for sale	30,500,000								30,500,000
Contractual balance of loans held for sale	$ 29,700,000								29,700,000
Net gain on sales of mortgage loans									$ 768,000