Investment Operations Mortgage Loans (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Carrying Value	$ 1,011,678	$ 1,039,829
Percent of Total	100.00%	100.00%
Year of origination 2019
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Carrying Value	$ 69,319
Percent of Total	6.80%
Year of origination 2018
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Carrying Value	$ 128,334	$ 137,519
Percent of Total	12.70%	13.20%
Year of origination 2017
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Carrying Value	$ 200,283	$ 207,540
Percent of Total	19.80%	20.00%
Year of origination 2016
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Carrying Value	$ 144,311	$ 149,437
Percent of Total	14.30%	14.40%
Year of origination 2015
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Carrying Value	$ 119,724	$ 128,877
Percent of Total	11.80%	12.40%
Year of origination prior
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Carrying Value	$ 349,707	$ 416,456
Percent of Total	34.60%	40.00%
0% - 50%
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Carrying Value	$ 412,973	$ 409,089
Percent of Total	40.80%	39.30%
51% - 60%
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Carrying Value	$ 310,869	$ 314,038
Percent of Total	30.70%	30.20%
61% - 70%
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Carrying Value	$ 256,280	$ 264,973
Percent of Total	25.40%	25.50%
71% - 80%
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Carrying Value	$ 31,556	$ 37,418
Percent of Total	3.10%	3.60%
81% - 90%
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Carrying Value	$ 0	$ 14,311
Percent of Total	0.00%	1.40%
South Atlantic
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Carrying Value	$ 288,299	$ 301,206
Percent of Total	28.50%	29.00%
Pacific
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Carrying Value	$ 164,996	$ 162,824
Percent of Total	16.30%	15.70%
East North Central
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Carrying Value	$ 117,053	$ 117,768
Percent of Total	11.60%	11.30%
West North Central
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Carrying Value	$ 108,942	$ 126,320
Percent of Total	10.80%	12.10%
Mountain
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Carrying Value	$ 96,857	$ 101,335
Percent of Total	9.60%	9.70%
East South Central
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Carrying Value	$ 81,275	$ 76,098
Percent of Total	8.00%	7.30%
West South Central
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Carrying Value	$ 76,650	$ 85,919
Percent of Total	7.60%	8.30%
Middle Atlantic
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Carrying Value	$ 45,687	$ 34,843
Percent of Total	4.50%	3.40%
New England
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Carrying Value	$ 31,919	$ 33,516
Percent of Total	3.10%	3.20%
Office
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Carrying Value	$ 417,746	$ 454,694
Percent of Total	41.30%	43.70%
Retail
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Carrying Value	$ 345,870	$ 332,579
Percent of Total	34.20%	32.00%
Industrial
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Carrying Value	$ 235,274	$ 234,453
Percent of Total	23.20%	22.60%
Other
SEC Schedule, 12-29, Real Estate Companies, Investment in Mortgage Loans on Real Estate [Line Items]
Carrying Value	$ 12,788	$ 18,103
Percent of Total	1.30%	1.70%