Summary of Significant Accounting Policies - Additional Information (Detail) (USD $)
 3 Months Ended 12 Months Ended
Mar. 31, 2014
Dec. 31, 2013
Summary Of Significant Accounting Policies [Line Items]    
Assets $ 7,275,395,000 $ 7,231,045,000
Liabilities 4,202,438,000 4,113,011,000
Reserves for uncollectible amounts 5,100,000 4,600,000
Accounts receivable 15,900,000 14,300,000
Provision for losses 10,800,000 9,600,000
Accrued rental revenue receivables 39,800,000 35,300,000
Allowance for loan losses 0 0
Loan placed on non accrual status, past due days   60 days
Restricted cash and deposits in escrow 45,103,000 58,691,000
Collateral deposits
    
Summary Of Significant Accounting Policies [Line Items]    
Restricted cash and deposits in escrow 21,865,000 [1] 21,816,000 [1]
Tenant improvements, repairs, and leasing commissions
    
Summary Of Significant Accounting Policies [Line Items]    
Restricted cash and deposits in escrow 11,455,000 [2] 10,297,000 [2]
Master trust release / title company escrow
    
Summary Of Significant Accounting Policies [Line Items]    
Restricted cash and deposits in escrow 7,456,000 [3] 21,893,000 [3]
Loan impounds
    
Summary Of Significant Accounting Policies [Line Items]    
Restricted cash and deposits in escrow 2,410,000 [4] 2,018,000 [4]
Other
    
Summary Of Significant Accounting Policies [Line Items]    
Restricted cash and deposits in escrow 1,917,000 [5] 2,667,000 [5]
Mortgages
    
Summary Of Significant Accounting Policies [Line Items]    
Loans on non accruals status 0 0
Notes
    
Summary Of Significant Accounting Policies [Line Items]    
Loans on non accruals status 0 0
Special Purpose Entity
    
Summary Of Significant Accounting Policies [Line Items]    
Assets 6,100,000,000 6,100,000,000
Liabilities $ 3,800,000,000 $ 3,800,000,000
[1] Funds held in reserve by lenders which, at their sole discretion, can be applied to the repayment of Debt. Any funds remaining on deposit after the debt is paid in full are released to the borrower.
[2] Deposits held by lenders that are reserved to fund tenant improvements/repairs on collateral properties or when leasing commissions are incurred to secure a new tenant.
[3] Reflects net sales proceeds from property dispositions held as collateral that can be released upon qualified re-investment.
[4] Funds held in lender controlled accounts generally used to meet future debt service or certain property cost requirements.
[5] Funds held in lender controlled accounts released within the following month after debt service requirements are met.