Regulatory and Capital Requirements - Additional Information (Detail) (USD $)						12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2012 NPRs Revised Current Regulatory Capital Rules [Member]	Dec. 31, 2012 Trust preferred securities [Member]	Dec. 31, 2011 Trust preferred securities [Member]	Dec. 31, 2012 Trust Preferred Securities [Member]	Dec. 31, 2012 Trust Preferred Securities [Member]
Schedule of Capitalization, Equity [Line Items]
Tier one risk-based capital to be well capitalized under prompt corrective action provision, ratio	6.00%
Risk-based Capital To Be Well Capitalized Under Prompt Corrective Action Provision, Ratio	10.00%
Tier one leverage capital to be well capitalized under prompt corrective action provision, ratio	5.00%
CET1 to risk-weighted assets, Basel III final framework	3.50%
Tier 1 capital to risk-weighted assets, Basel III final framework	4.50%
Total capital to risk-weighted assets, Basel III final framework	8.00%
Revised NPRs asset value	$ 613,471,000	$ 557,210,000	$ 500,000,000
Tier one capital				186,300,000	176,300,000
Net increase in capital							10,000,000
Trust preferred securities assumed in acquisition						20,000,000
Redemption						$ 10,000,000