Retirement Plans - Additional Information (Detail)	9 Months Ended
	Sep. 30, 2013
Directors' Retirement Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Annual retirement benefit age	75 years
SERP [Member]
Defined Benefit Plan Disclosure [Line Items]
Annual retirement benefit age	65 years
Annual retirement benefit percentage	25.00%
Credited service description	Twenty or more years
Credited service	1 year
Number of payments	Lump sum or ten equal annual payments
Benefit payable upon early retirement	Age 50 with at least twelve years of service
Service needed to lesser benefit payable upon early retirement	12 years
Maximum [Member] | Directors' Retirement Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Service period to get retirement benefit	10 years
Retirement benefit calculation ratio	80.00%
Years of service required for ratios	20 years
Maximum [Member] | SERP [Member]
Defined Benefit Plan Disclosure [Line Items]
Final average pay multiplied by a ratio	25.00%
Participants credited service under benefit plans	34 years
Minimum [Member] | Directors' Retirement Plan [Member]
Defined Benefit Plan Disclosure [Line Items]
Service period to get retirement benefit	5 years
Retirement benefit calculation ratio	25.00%
Years of service required for ratios	10 years
Minimum [Member] | SERP [Member]
Defined Benefit Plan Disclosure [Line Items]
Final average pay multiplied by a ratio	1.25%
Participants credited service under benefit plans	22 years