Income Taxes (Detail) (USD $) In Thousands, unless otherwise specified	9 Months Ended	12 Months Ended
	Sep. 30, 2012	Dec. 31, 2011
Income Tax Contingency [Line Items]
Minimum annual distribution of adjusted taxable income for REIT qualification	90.00%
Income tax benefit	$ 612
Net deferred tax assets		60,197
Internal Revenue Service (IRS) [Member]
Income Tax Contingency [Line Items]
Unrecognized tax benefits, increases resulting from prior period tax positions	$ 797	$ 797