Fair Value of Financial Instruments - Equity Interest in Related Party and Related Loans Measured at Fair Value on Recurring Basis (Detail) $ in Thousands	Sep. 30, 2017 USD ($)
Financial Instruments Measured At Fair Value On Recurring Basis [Line Items]
Fair Value	$ 233,698
Cost	233,698
Fair Value Measurements, Recurring [Member] | Equity investments [Member] | Other Assets [Member]
Financial Instruments Measured At Fair Value On Recurring Basis [Line Items]
Fair Value	3,300
Cost	3,300
Fair Value Measurements, Recurring [Member] | Acquisition and Other Loans [Member] | Other Loans [Member]
Financial Instruments Measured At Fair Value On Recurring Basis [Line Items]
Fair Value	115,398
Cost	115,398
Fair Value Measurements, Recurring [Member] | Mortgage Loans [Member] | Mortgage Loans [Member]
Financial Instruments Measured At Fair Value On Recurring Basis [Line Items]
Fair Value	115,000
Cost	$ 115,000