Derivative Instruments and Hedging Activities - Additional Information (Detail) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	May 14, 2013 Swap	May 31, 2013 Swap	Aug. 23, 2012 Swap
Derivative Instruments, Gain (Loss) [Line Items]
Number of restructured interest rate swaps			2
Reclassified as an increase to interest expense, expected during the next 12 months	$ 2,510,000
Tax expense on unrealized gain (loss) on derivatives	(286,000)	632,000
Termination value of derivatives in a net liability position	662,000
Collateral posted relating to credit risk-related contingent features	0
Interest Rate Swaps [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Notional amount of interest rate swap	1,000,000,000				550,000,000
Number of outstanding interest rate derivatives	3			2	2
Not Designated as Hedge Accounting Relationships [Member]
Derivative Instruments, Gain (Loss) [Line Items]
Derivatives outstanding	$ 0	$ 0