Related Party Transactions (Detail) (USD $)	9 Months Ended	12 Months Ended
	Sep. 30, 2010	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Related Party Transaction [Line Items]
Payments for life insurance policies		$ 284,000	$ 284,000	$ 478,000
Management [Member]
Related Party Transaction [Line Items]
Related party transaction, expenses from transactions with related party		2,000	66,000	560,000
Immediate Family Member of Management or Principal Owner [Member]
Related Party Transaction [Line Items]
Related party transaction, expenses from transactions with related party	859,000	44,000	48,000	48,000
Related Customer [Member] | Management [Member]
Related Party Transaction [Line Items]
Charges to related party		527,000	480,000	463,000
Related party receivables		907,000	860,000
Related party revenues		1,214,000	1,123,000	979,000
Accounts receivable, related party		1,232,000	775,000
Deferred Compensation, Excluding Share-based Payments and Retirement Benefits [Member] | Management [Member]
Related Party Transaction [Line Items]
Estimated fair value of life insurance policies		8,700,000	7,900,000
Deferred Compensation, Excluding Share-based Payments and Retirement Benefits [Member] | Board of Directors Chairman [Member]
Related Party Transaction [Line Items]
Life insurance, split dollar policies, face amount		200,000,000
Payments for life insurance policies		284,000	284,000	284,000
Deferred Compensation, Excluding Share-based Payments and Retirement Benefits [Member] | Chief Executive Officer [Member]
Related Party Transaction [Line Items]
Life insurance, split dollar policies, face amount		11,000,000
Payments for life insurance policies		$ 0	$ 0	$ 115,000