Long-Term Debt - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011
Debt Instrument [Line Items]
Term for credit facility	5 years
Minimum percentage of owned subsidiaries	100.00%
Letter of Credit [Member]
Debt Instrument [Line Items]
Limit for the issuance of standby letters of credit	$ 7.5
Revolving Credit Facility [Member]
Debt Instrument [Line Items]
Borrowing capacity	75.0
Credit facility amount increase provision on condition	50
Credit Facility amount outstanding	$ 15.0	$ 15.0
Credit Facility Interest Periods	1, 2, 3 or 6 months
Credit facility Interest rate	2.35%
Minimum percentage of owned subsidiaries	100.00%
Acquisitions	Less than 100% owned subsidiaries
Minimum interest coverage ratio	At least 4.00:1
Minimum percentage of interest adjustment	4.00
Leverage ratio	No greater than 2.75:1
Maximum percentage of indebtedness	2.75
Revolving Credit Facility [Member] | Maximum [Member]
Debt Instrument [Line Items]
percentage of margin on principal amount, maximum	2.50%
Commitment fee, maximum	0.50%
Revolving Credit Facility [Member] | Minimum [Member]
Debt Instrument [Line Items]
percentage of margin on principal amount, maximum	0.75%
Commitment fee, maximum	0.35%