Real Estate and Other Investments - Investment Real Estate by Property-Type and Geographic Distribution (Detail) - Real estate - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2020	Dec. 31, 2019
Concentration Risk [Line Items]
Real estate investments	$ 545,646	$ 551,219
East North Central
Concentration Risk [Line Items]
Real estate investments	32,818	32,539
East South Central
Concentration Risk [Line Items]
Real estate investments	33,864	34,248
Mountain
Concentration Risk [Line Items]
Real estate investments	67,719	68,498
Pacific
Concentration Risk [Line Items]
Real estate investments	39,911	40,462
South Atlantic
Concentration Risk [Line Items]
Real estate investments	83,079	83,552
West South Central
Concentration Risk [Line Items]
Real estate investments	274,967	278,833
Other
Concentration Risk [Line Items]
Real estate investments	13,288	13,087
Industrial
Concentration Risk [Line Items]
Real estate investments	69,051	68,809
Office
Concentration Risk [Line Items]
Real estate investments	216,464	219,490
Retail
Concentration Risk [Line Items]
Real estate investments	215,142	215,800
Other
Concentration Risk [Line Items]
Real estate investments	$ 44,989	$ 47,120
Property Type Concentration Risk
Concentration Risk [Line Items]
Distribution, percentage	100.00%	100.00%
Property Type Concentration Risk | Industrial
Concentration Risk [Line Items]
Distribution, percentage	12.70%	12.50%
Property Type Concentration Risk | Office
Concentration Risk [Line Items]
Distribution, percentage	39.70%	39.80%
Property Type Concentration Risk | Retail
Concentration Risk [Line Items]
Distribution, percentage	39.40%	39.10%
Property Type Concentration Risk | Other
Concentration Risk [Line Items]
Distribution, percentage	8.20%	8.60%
Geographic Distribution
Concentration Risk [Line Items]
Distribution, percentage	100.00%	100.00%
Geographic Distribution | East North Central
Concentration Risk [Line Items]
Distribution, percentage	6.00%	5.90%
Geographic Distribution | East South Central
Concentration Risk [Line Items]
Distribution, percentage	6.20%	6.20%
Geographic Distribution | Mountain
Concentration Risk [Line Items]
Distribution, percentage	12.40%	12.40%
Geographic Distribution | Pacific
Concentration Risk [Line Items]
Distribution, percentage	7.30%	7.30%
Geographic Distribution | South Atlantic
Concentration Risk [Line Items]
Distribution, percentage	15.20%	15.20%
Geographic Distribution | West South Central
Concentration Risk [Line Items]
Distribution, percentage	50.40%	50.60%
Geographic Distribution | Other
Concentration Risk [Line Items]
Distribution, percentage	2.50%	2.40%