Condensed Statement of Operations (Parent Company) (Detail) (USD $) In Thousands, except Share data, unless otherwise specified	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Income Statement [Abstract]
Income (loss) from investment in the Partnership	$ 3,250	$ 0	$ 0
General and Administrative Expense	65,083	55,516	51,172
Operating income (loss)	34,829	74,473	73,913
Interest and other income	5,054	707	294
Income (loss) before income taxes	(43,382)	(4,047)	(27,534)
Income tax benefit	6,642	2,768	6,021
Net loss	(36,740)	(1,279)	(21,513)
Net loss per common share:
Basic and diluted common units	$ (0.26)	$ (0.12)	$ (0.24)
Weighted average shares outstanding:
Basic	47,384,000	47,150,000	46,732,000
Diluted	47,384,000	47,150,000	46,732,000
Parent Company [Member]
Income Statement [Abstract]
Income (loss) from investment in the Partnership	(16,080)	(7,192)	(16,042)
General and Administrative Expense	(3,775)	(2,715)	(2,758)
Operating income (loss)	(19,855)	(9,907)	(18,800)
Interest and other income	7	6	7
Income (loss) before income taxes	(19,848)	(9,901)	(18,793)
Income tax benefit	(7,367)	(3,894)	(7,142)
Net loss	$ (12,481)	$ (6,007)	$ (11,651)
Net loss per common share:
Basic and diluted common units	$ (0.26)	$ (0.12)	$ (0.24)
Weighted average shares outstanding:
Basic	47,384	47,150	46,732
Diluted	47,384	47,150	46,732