Short-Term Borrowing - Additional Information (Detail) (USD $)	12 Months Ended		1 Months Ended	12 Months Ended	1 Months Ended		12 Months Ended
	Dec. 31, 2012 CreditFacility	Dec. 31, 2011	Jun. 22, 2012 Unsecured bank lines of credit [Member] CreditFacility	Dec. 31, 2012 Unsecured bank lines of credit [Member] CreditFacility Institution	Jun. 22, 2012 Unsecured bank lines of credit [Member] LIBOR [Member]	Jun. 22, 2012 Unsecured bank lines of credit [Member] Lender's base rate [Member]	Dec. 31, 2012 Revolving credit facility [Member]	Dec. 31, 2012 Revolving credit facility [Member] LIBOR [Member]	Dec. 31, 2012 Revolving credit facility [Member] Lender's base rate [Member]	Dec. 31, 2012 Second facility [Member]	Dec. 31, 2012 Uncommitted credit facilities [Member] CreditFacility	Dec. 31, 2012 Uncommitted line of credit first facility [Member]	Dec. 31, 2012 Uncommitted line of credit second facility [Member]
Short-term Debt [Line Items]
Short-term borrowings	$ 61,199,000	$ 34,707,000
Annual weighted average interest rates on short-term borrowings	1.48%	1.53%
Commitment fees	73,000	85,000
Lines of credit outstanding amount	56,400,000	30,500,000					60,000,000
Book overdrafts	4,800,000	4,200,000
Number of unsecured bank lines of credit			4	5
Number of financial institutions, unsecured bank lines of credit				2
Lines of credit outstanding amount			40,000,000	140,000,000			40,000,000
Revolving credit note, matures			October 31, 2013				October 31, 2013
Maximum Aggregate Short Term Borrowing Authorized by our Board of Directors				100,000,000
Number of committed revolving credit facilities	2
Unsecured revolving line of credit							30,000,000			30,000,000
Line of credit facility, interest description					LIBOR plus 80 basis points	Lender's base rate plus 80 basis points		LIBOR rate, plus 1.25 percent	Base rate plus 1.25 percent
Amount available under uncommitted credit facility										13,600,000	30,000,000	20,000,000	15,700,000
Funded indebtedness ratio	0.65
Fixed charge coverage ratio, maximum	1.20
Fixed charge coverage ratio, minimum	1.0
Number of uncommitted line-of-credit facilities											2
Uncommitted line of credit											40,000,000	20,000,000	20,000,000
Letters of credit issued	4,300,000
Amount of letter of credit reduced	$ 4,300,000