Income Taxes - Additional Information (Detail) - USD ($)	3 Months Ended		9 Months Ended	12 Months Ended
	Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Dec. 31, 2014
Income Taxes [Line Items]
Total income tax expense (benefit), rate	24.40%	24.10%
Combined federal and state statutory tax rate			37.20%
Federal deferred tax asset	$ 190,000,000	$ 153,000,000	$ 190,000,000	$ 174,000,000
State deferred tax asset	26,000,000	19,000,000	26,000,000	20,000,000
Valuation allowance		1,000,000
Reduction in deferred tax assets	2,800,000	$ 1,000,000		1,000,000
Maximum [Member]
Income Taxes [Line Items]
Valuation allowance	$ 1,000,000		$ 1,000,000	$ 1,000,000