Equity (Details) (USD $)	0 Months Ended	12 Months Ended			1 Months Ended		12 Months Ended			1 Months Ended			0 Months Ended	3 Months Ended	12 Months Ended	3 Months Ended	12 Months Ended	3 Months Ended	12 Months Ended
	Feb. 14, 2011	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011	Mar. 31, 2011 Restricted Stock	Jan. 31, 2011 Restricted Stock Installment	Dec. 31, 2013 Restricted Stock	Jun. 13, 2013 Restricted Stock	Jul. 10, 2012 Restricted Stock	Jan. 31, 2011 Restricted Stock Non Employee Directors Installment	Jan. 31, 2011 Time Based Restricted Stock Executive Officers	Jan. 31, 2011 Performance Based Restricted Stock Executive Officers	May 06, 2013 At The Market Equity Program Agent	Dec. 31, 2013 At The Market Equity Program	Dec. 31, 2013 At The Market Equity Program	Dec. 31, 2013 Commissions At The Market Equity Program	Dec. 31, 2013 Commissions At The Market Equity Program	Dec. 31, 2013 Other Offering Costs At The Market Equity Program	Dec. 31, 2013 Other Offering Costs At The Market Equity Program
Equity [Line Items]
Number of sales agents for the at-the-market equity program													4
Aggregate offering price for the at-the-market equity program													$ 150,000,000.0
Common stock, shares issued	251,050													22,738	741,452
Weighted average price per share														$ 32.25	$ 35.00
Proceeds from issuance of common stock, net		25,348,000	0	596,541,000										700,000	26,000,000
Payments of stock issuance costs																10,000	300,000	100,000	800,000
Remaining capacity available for issuance														124,000,000	124,000,000
Noncontrolling common units		17,917,109
Percentage of ownership interests classified as noncontrolling		31.00%
Proceeds from private placement of common units	5,400,000	0	0	5,410,000
Shares of common stock		106,236	372,654
Preferred stock, shares authorized		10,000,000
Preferred stock, par-value		$ 0.01
Equity incentive award plan, common stock authorized for issuance		4,054,411
Equity incentive award plan, common stock available for future issuance		3,425,353
Equity incentive award plan, granted					123,950					1,951	198,000	297,000
Equity incentive award plan, fair value					1,600,000					200,000	4,100,000	3,900,000
Performance period to which performance-based vesting is subject, years						3 years
Vesting installments of restricted shares						2
Restricted stock granted										one-third
Restricted stock awards ratable vesting periods (First installment)										3
Restricted shares granted to members for board (in shares)								5,004	8,015
Noncash compensation expense recognized		2,800,000	2,900,000	2,600,000
Unrecognized compensation expense		$ 1,600,000
Unrecognized compensation expense, weighted-average recognition period (in years)							7 months 2 days
Weighted average unvested shares outstanding		630,130	629,493	578,489