Accumulated Other Comprehensive Income - Components of Accumulated OCI and the Ending Balances (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended						9 Months Ended		12 Months Ended
	Sep. 30, 2013	Jun. 30, 2013	Mar. 31, 2013	Sep. 30, 2012	Jun. 30, 2012	Mar. 31, 2012	Sep. 30, 2013	Sep. 30, 2012	Dec. 31, 2012
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated other comprehensive income, Beginning balance			$ 1,258			$ 1,745	$ 1,258	$ 1,745	$ 1,745
Other comprehensive income	(2,260)	(1,747)	182	872	(658)	363	(3,825)	(577)	(487)
Accumulated other comprehensive income, Ending balance	(2,567)			2,322			(2,567)	2,322	1,258
Unrealized Gains on Securities [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated other comprehensive income, Beginning balance			2,189			919	2,189	919	919
Other comprehensive income	(2,110)	(2,397)	219	1,503	427	321
Accumulated other comprehensive income, Ending balance	(2,099)			3,170			(2,099)	3,170
Unrealized Gains (Losses) on Derivatives [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Accumulated other comprehensive income, Beginning balance			(931)			826	(931)	826	826
Other comprehensive income	(150)	650	(37)	(631)	(1,085)	42
Accumulated other comprehensive income, Ending balance	$ (468)			$ (848)			$ (468)	$ (848)