Fair Value of Financial Instruments - Equity Interest in Related Party and Related Loans Measured at Fair Value on Recurring Basis (Detail) - USD ($) $ in Thousands	Dec. 31, 2016	Dec. 31, 2015
Financial Instruments Measured At Fair Value On Recurring Basis [Line Items]
Fair Value	$ 232,434	$ 920,901
Cost	232,434	920,901
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	7,349
Cost	3,300	7,349
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	116,298	603,552
Cost	116,298	603,552
Fair Value Measurements, Recurring [Member] | Mortgage Loans [Member] | Mortgage Loans [Member]
Financial Instruments Measured At Fair Value On Recurring Basis [Line Items]
Fair Value	112,836	310,000
Cost	$ 112,836	$ 310,000