Comprehensive Income and Accumulated Other Comprehensive Income - Schedule of Changes in Accumulated Other Comprehensive Income (AOCI) (Detail) (USD $) In Thousands, unless otherwise specified	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	$ 2,434		$ 2,979
Other comprehensive income (loss) before reclassifications	(4,448)		(4,867)
Amounts reclassified from accumulated other comprehensive income	388		262
Net current-period other comprehensive income (loss)	(4,060)	503	(4,605)	450
Ending balance	(1,626)		(1,626)
Changes in Net Unrealized Gains on Investment Securities Having No Credit Losses Recognized in the Consolidated Statement of Income [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	2,421		2,966
Other comprehensive income (loss) before reclassifications	(4,448)		(4,867)
Amounts reclassified from accumulated other comprehensive income	388		262
Net current-period other comprehensive income (loss)	(4,060)		(4,605)
Ending balance	(1,639)		(1,639)
Changes in Net Unrealized Gains on Investment Securities Having Credit Losses Recognized in the Consolidated Statement of Income [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	13		13
Other comprehensive income (loss) before reclassifications
Amounts reclassified from accumulated other comprehensive income
Net current-period other comprehensive income (loss)
Ending balance	$ 13		$ 13