Loans Receivable, Net - Overall Statistics for Loans Receivable Portfolio (Detail) $ in Thousands	12 Months Ended
	Dec. 31, 2018 USD ($) SecurityLoan	Dec. 31, 2017 USD ($) SecurityLoan	Dec. 31, 2016 USD ($)
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of Loans | SecurityLoan	125	110
Net book value	$ 14,191,200	$ 10,056,732
Loans Receivable [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Number of Loans | SecurityLoan	125	110
Principal balance	$ 14,293,970	$ 10,108,226	$ 8,727,218
Unfunded loan commitments	$ 3,405,945	$ 1,573,107
Weighted-average maximum maturity (years)	3 years 10 months 24 days	3 years 6 months
Loans Receivable [Member] | LIBOR [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Weighted-average cash coupon, rate	5.67%	5.55%
Weighted-average all-in yield, rate	6.00%	5.95%
Net Book Value [Member]
Accounts, Notes, Loans and Financing Receivable [Line Items]
Net book value	$ 14,191,200	$ 10,056,732	$ 8,692,978