Securities Available-for-Sale - Additional Information (Detail) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2012 Securities	Dec. 31, 2011 Securities	Dec. 31, 2010
Schedule of Available-for-sale Securities [Line Items]
Securities in Continuous Unrealized Loss Position For 12 Months or Longer		$ 736
Management booked impairment of private-label mortgage-backed securities		10	226
Amortized Cost	380,454	340,782
Projected average life of securities portfolio	4 years 1 month 6 days
Projected average life of portfolio modified duration	3 years 8 months 12 days
Number of investment securities sold	0	35
Proceeds from investment securities sold		36,425
Gross realized gains from investment securities sold		1,134
Gross realized losses from investment securities sold		250
Securities pledged as collateral [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	24,136
Estimated market value of pledged securities	25,044
Substandard [Member]
Schedule of Available-for-sale Securities [Line Items]
Amortized Cost	3,281	3,644	8,400
Private-label mortgage-backed securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Management booked impairment of private-label mortgage-backed securities		10
Number of private-label mortgage-backed securities		1
Unrealized Loss Positions [Member]
Schedule of Available-for-sale Securities [Line Items]
Investment securities in unrealized loss positions, number of positions	20	91
Securities in Continuous Unrealized Loss Position For 12 Months or Longer	19,851	4,042
Available for sale securities in continuous loss positions for twelve months or longer number, of positions	604
Amortized Cost	111,473	101,904
Unrealized Loss Positions [Member] | Private-label mortgage-backed securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Securities in Continuous Unrealized Loss Position For 12 Months or Longer	2,696	2,477
Available for sale securities in continuous loss positions for twelve months or longer number, of positions	435
Amortized Cost	3,130	5,590
Unrealized Loss Positions [Member] | Private-label mortgage-backed securities [Member] | Substandard [Member]
Schedule of Available-for-sale Securities [Line Items]
Number of private-label mortgage-backed securities	8
Unrealized Loss Positions [Member] | Mortgage-backed securities [Member]
Schedule of Available-for-sale Securities [Line Items]
Securities in Continuous Unrealized Loss Position For 12 Months or Longer	17,155	1,565
Available for sale securities in continuous loss positions for twelve months or longer number, of positions	169
Amortized Cost	$ 95,803	$ 94,314