Loans Receivable - Additional Information (Detail)	6 Months Ended
	Jun. 30, 2016 USD ($)	Dec. 31, 2015 USD ($)
Accounts, Notes, Loans and Financing Receivable [Line Items]
Weighted-average risk rating on loan exposure	2.3	2.2
Impaired loans	$ 0	$ 0
Maturity date	Aug. 31, 2016
Partial repayment of loan on sale of collateralized assets	$ 102,600,000
Net book value of loan after partial repayment	$ 9,090,934,000	9,077,007,000
Extend maturity term	6 months
Net Book Value [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Net book value of loan after partial repayment	$ 9,090,934,000	9,077,007,000
Risk Rating 4 [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Principal Balance of collateralized loan	113,300,000
Risk Rating 4 [Member] | Net Book Value [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Net book value of loan after partial repayment	$ 10,300,000	$ 113,038,000