Fair Value Measurements - Impaired Loans Remeasured and Reported at Fair Value of Underlying Collateral (Detail) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012	Sep. 30, 2013 Level 2 [Member]	Sep. 30, 2012 Level 2 [Member]	Sep. 30, 2013 Level 3 [Member]	Sep. 30, 2012 Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Carrying value of impaired loans before allocations	$ 69,776	$ 80,397	$ 13,870	$ 13,227	$ 4,430	$ 384
Specific valuation allowance allocations	(8,949)	(8,237)	(2,098)	(2,922)	(2,370)	(61)
Fair value			$ 11,772	$ 10,305	$ 2,060	$ 323