Income Taxes - Additional Information (Detail) - USD ($)	3 Months Ended			9 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Mar. 31, 2014	Sep. 30, 2015	Sep. 30, 2014	Dec. 31, 2014	Jan. 27, 2014	Dec. 31, 2013
Income Tax Examination [Line Items]
Unrecognized tax benefits	$ 0			$ 0
Income tax examination				Federal and state tax returns for the 2012 through 2014 tax years are subject to examination
Income tax examination in process				No state income tax return examinations are currently in process.
Amortization of low-income housing credit investments reflected as income tax expense	477,000	$ 294,000		$ 1,400,000	$ 881,000
Tax benefits recorded as income tax expense				223,000
Carrying value of investment in affordable housing credits	11,400,000			$ 11,400,000		$ 13,000,000
Earliest Tax Year [Member]
Income Tax Examination [Line Items]
Income tax examination period				2012
Latest Tax Year [Member]
Income Tax Examination [Line Items]
Income tax examination period				2014
Tax Credit [Member]
Income Tax Examination [Line Items]
Affordable housing tax credits	$ 1,500,000			$ 1,500,000
SASCO [Member]
Income Tax Examination [Line Items]
Deferred tax asset								$ 4,900,000
Deferred tax asset valuation allowance							$ 4,900,000
Deferred tax liabilities								$ 1,800,000
Income tax benefit			$ (6,700,000)
SASCO [Member] | Eliminated [Member]
Income Tax Examination [Line Items]
Deferred tax liabilities							$ 1,800,000