Income Taxes - Narrative (Detail) (USD $) In Millions, unless otherwise specified	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Income Taxes:
Income tax expense for income and the portion of earnings retained based on 162(m) limitations		$ 22.1	$ 44.1
Years federal and state tax returns remain open for examination	2012, 2011 and 2010
Real Estate Investment Trust
Income Taxes:
REIT Taxable income distributed	100.00%
Income tax expense for income and the portion of earnings retained based on 162(m) limitations	$ 8.2	$ 13.8	$ 14.9