Equity (Details Textual) (USD $) In Millions, except Share data, unless otherwise specified	0 Months Ended	3 Months Ended	9 Months Ended
	Jan. 19, 2011	Sep. 30, 2012	Sep. 30, 2012 Installment Anniversary	Sep. 30, 2011	Jul. 10, 2012	Jan. 19, 2012	Mar. 16, 2011
Equity (Textual) [Abstract]
Restricted stock granted			one-third
Performance period to which performance-based vesting is subject, years	3 years		3 years
Noncash compensation expense			$ 2.1	$ 1.9
Unrecognized compensation expense		$ 5.1	$ 5.1
Equity (Additional Textual) [Abstract]
Vesting installments of restricted shares			2
Noncontrolling common units		18,371,186	18,371,186
Shares of common stock			24,903
Common stock price per share			$ 26.21
Percentage of ownership interests classified as noncontrolling		32.00%	32.00%
Restricted stock awards ratable vesting periods (First installment)			3
Restricted stock awards ratable vesting periods (Second installment)			4
Grant Shares Date						Jan. 19, 2012	Mar. 16, 2011
Weighted average unvested shares outstanding		632,438	628,240
Restricted shares granted to members for board					8,015
Restricted stock [Member]
Equity (Textual) [Abstract]
Performance period to which performance-based vesting is subject, years			3 years