Executive Benefit Agreements and Employee Savings Plans - Executive Benefit Agreements (Detail) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2012	Dec. 31, 2011
Executive Benefit Agreements and Employee Savings Plans [Line Items]
Accrued death benefits-All agreements	$ 4,185	$ 4,017
Total undiscounted executive benefits-1992 Agreements	1,928	1,950
Discount rates utilized-1992 Agreements	2.78%	3.58%
Accrued executive benefits-1992 Agreements	1,365	1,262
Death Benefit 1981 Agreements [Member]
Executive Benefit Agreements and Employee Savings Plans [Line Items]
Undiscounted death benefits	3,865	4,115
Death Benefit 1992 Agreements [Member]
Executive Benefit Agreements and Employee Savings Plans [Line Items]
Undiscounted death benefits	302	302
Death Benefit 2005 Agreement [Member]
Executive Benefit Agreements and Employee Savings Plans [Line Items]
Undiscounted death benefits	$ 2,500	$ 2,500