Swapped Variable Cost for Fixed Cost and Terms of Interest Rate Swap Agreements (Detail) (Interest rate swaps, USD $) In Thousands, unless otherwise specified			9 Months Ended
	Sep. 30, 2012	Dec. 31, 2011	Sep. 30, 2012 Contract, One	Sep. 30, 2012 Contract, Two	Sep. 30, 2012 Contract, Three	Sep. 30, 2012 Contract, Four	Sep. 30, 2012 Contract, Five
Derivative [Line Items]
Notional Amount	$ 43,000	$ 43,000	$ 10,000	$ 10,000	$ 10,000	$ 5,000	$ 8,000
Fixed Cost			5.09%	5.84%	5.71%	4.35%	4.14%
Maturity Date			Jun. 30, 2021	Jun. 30, 2029	Jun. 30, 2030	Mar. 30, 2031	Jul. 07, 2031