Real Estate and Other Investments - Carrying Amount and Maximum Exposure to Loss Related to VIEs (Detail) - VIE, Not Primary Beneficiary - USD ($) $ in Thousands	Dec. 31, 2018	Dec. 31, 2017
Mortgage Loans
Variable Interest Entity [Line Items]
Carrying Amount	$ 633,533	$ 493,014
Maximum Exposure to Loss	633,533	493,014
Investments in Unconsolidated Affiliates
Variable Interest Entity [Line Items]
Carrying Amount	330,730	314,808
Maximum Exposure to Loss	330,730	314,808
Accrued Investment Income
Variable Interest Entity [Line Items]
Carrying Amount	2,191	1,817
Maximum Exposure to Loss	$ 2,191	$ 1,817