Long-Term Debt - Additional Information (Detail) (USD $)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Jul. 31, 2008	Dec. 31, 2012 July 31, 2008 Term Loan	Dec. 31, 2012 July 31, 2008 Term Loan Percentage Over Libor	Jan. 31, 2009 July 31, 2008 Term Loan Percentage Over Libor	Jul. 31, 2008 July 31, 2008 Term Loan Percentage Over Libor	Jul. 31, 2008 July 31, 2008 Term Loan Prime Rate
Debt Instrument [Line Items]
Borrowed from syndicate of banks				$ 355,000,000
Fixed portion of the variable rate						0.75%	0.75%	1.50%	0.50%
Aggregate principal payments	74,408,000	31,889,000	65,630,000
Interest rate on term loan	1.22%	1.05%	1.53%
Weighted average interest rate	1.08%
Long-term Debt	$ 53,149,000	$ 127,557,000
Variable interest rate					1.06%