Mortgage Loans on Real Estate (Aging of Financing Receivables) (Details) - USD ($) $ in Thousands	Mar. 31, 2023	Dec. 31, 2022
Commercial Mortgage Loans
Financing Receivable, Past Due [Line Items]
Amortized cost, year one, originated in current fiscal year	$ 7,788	$ 425,875
Amortized cost, year two, originated in fiscal year before current fiscal year	461,509	592,468
Amortized cost, year three, originated two years before current fiscal year	600,590	486,339
Amortized cost, year four, originated three years before current fiscal year	479,951	591,076
Amortized cost, year five, originated four years before current fiscal year	581,416	416,132
Amortized cost, originated more than five years before current fiscal year	1,432,653	1,042,668
Mortgage loans, amortized cost	3,563,907	3,554,558
Commercial Mortgage Loans | Current
Financing Receivable, Past Due [Line Items]
Amortized cost, year one, originated in current fiscal year	7,788	425,875
Amortized cost, year two, originated in fiscal year before current fiscal year	461,509	592,468
Amortized cost, year three, originated two years before current fiscal year	600,590	486,339
Amortized cost, year four, originated three years before current fiscal year	479,951	591,076
Amortized cost, year five, originated four years before current fiscal year	581,416	416,132
Amortized cost, originated more than five years before current fiscal year	1,432,653	1,042,668
Mortgage loans, amortized cost	3,563,907	3,554,558
Commercial Mortgage Loans | 30 - 59 days past due
Financing Receivable, Past Due [Line Items]
Amortized cost, year one, originated in current fiscal year	0	0
Amortized cost, year two, originated in fiscal year before current fiscal year	0	0
Amortized cost, year three, originated two years before current fiscal year	0	0
Amortized cost, year four, originated three years before current fiscal year	0	0
Amortized cost, year five, originated four years before current fiscal year	0	0
Amortized cost, originated more than five years before current fiscal year	0	0
Mortgage loans, amortized cost	0	0
Commercial Mortgage Loans | 60 - 89 days past due
Financing Receivable, Past Due [Line Items]
Amortized cost, year one, originated in current fiscal year	0	0
Amortized cost, year two, originated in fiscal year before current fiscal year	0	0
Amortized cost, year three, originated two years before current fiscal year	0	0
Amortized cost, year four, originated three years before current fiscal year	0	0
Amortized cost, year five, originated four years before current fiscal year	0	0
Amortized cost, originated more than five years before current fiscal year	0	0
Mortgage loans, amortized cost	0	0
Commercial Mortgage Loans | Over 90 days past due
Financing Receivable, Past Due [Line Items]
Amortized cost, year one, originated in current fiscal year	0	0
Amortized cost, year two, originated in fiscal year before current fiscal year	0	0
Amortized cost, year three, originated two years before current fiscal year	0	0
Amortized cost, year four, originated three years before current fiscal year	0	0
Amortized cost, year five, originated four years before current fiscal year	0	0
Amortized cost, originated more than five years before current fiscal year	0	0
Mortgage loans, amortized cost	0	0
Agricultural Mortgage Loans
Financing Receivable, Past Due [Line Items]
Amortized cost, year one, originated in current fiscal year	41,988	196,347
Amortized cost, year two, originated in fiscal year before current fiscal year	195,288	160,641
Amortized cost, year three, originated two years before current fiscal year	158,366	169,346
Amortized cost, year four, originated three years before current fiscal year	172,036	5,629
Amortized cost, year five, originated four years before current fiscal year	5,589	34,000
Amortized cost, originated more than five years before current fiscal year	34,000	0
Mortgage loans, amortized cost	607,267	565,963
Agricultural Mortgage Loans | Current
Financing Receivable, Past Due [Line Items]
Amortized cost, year one, originated in current fiscal year	41,988	196,347
Amortized cost, year two, originated in fiscal year before current fiscal year	195,288	160,641
Amortized cost, year three, originated two years before current fiscal year	153,023	166,211
Amortized cost, year four, originated three years before current fiscal year	172,036	5,629
Amortized cost, year five, originated four years before current fiscal year	5,589	34,000
Amortized cost, originated more than five years before current fiscal year	34,000	0
Mortgage loans, amortized cost	601,924	562,828
Agricultural Mortgage Loans | 30 - 59 days past due
Financing Receivable, Past Due [Line Items]
Amortized cost, year one, originated in current fiscal year	0	0
Amortized cost, year two, originated in fiscal year before current fiscal year	0	0
Amortized cost, year three, originated two years before current fiscal year	0	0
Amortized cost, year four, originated three years before current fiscal year	0	0
Amortized cost, year five, originated four years before current fiscal year	0	0
Amortized cost, originated more than five years before current fiscal year	0	0
Mortgage loans, amortized cost	0	0
Agricultural Mortgage Loans | 60 - 89 days past due
Financing Receivable, Past Due [Line Items]
Amortized cost, year one, originated in current fiscal year	0	0
Amortized cost, year two, originated in fiscal year before current fiscal year	0	0
Amortized cost, year three, originated two years before current fiscal year	0	0
Amortized cost, year four, originated three years before current fiscal year	0	0
Amortized cost, year five, originated four years before current fiscal year	0	0
Amortized cost, originated more than five years before current fiscal year	0	0
Mortgage loans, amortized cost	0	0
Agricultural Mortgage Loans | Over 90 days past due
Financing Receivable, Past Due [Line Items]
Amortized cost, year one, originated in current fiscal year	0	0
Amortized cost, year two, originated in fiscal year before current fiscal year	0	0
Amortized cost, year three, originated two years before current fiscal year	5,343	3,135
Amortized cost, year four, originated three years before current fiscal year	0	0
Amortized cost, year five, originated four years before current fiscal year	0	0
Amortized cost, originated more than five years before current fiscal year	0	0
Mortgage loans, amortized cost	5,343	3,135
Residential Mortgage Loans
Financing Receivable, Past Due [Line Items]
Amortized cost, year one, originated in current fiscal year	224,031	1,970,718
Amortized cost, year two, originated in fiscal year before current fiscal year	2,027,790	624,834
Amortized cost, year three, originated two years before current fiscal year	580,981	233,741
Amortized cost, year four, originated three years before current fiscal year	207,065	31,262
Amortized cost, year five, originated four years before current fiscal year	29,268	4,506
Amortized cost, originated more than five years before current fiscal year	4,542	417
Mortgage loans, amortized cost	3,073,677	2,865,478
Residential Mortgage Loans | Current
Financing Receivable, Past Due [Line Items]
Amortized cost, year one, originated in current fiscal year	224,031	1,915,169
Amortized cost, year two, originated in fiscal year before current fiscal year	2,003,711	595,363
Amortized cost, year three, originated two years before current fiscal year	562,310	211,119
Amortized cost, year four, originated three years before current fiscal year	194,720	27,483
Amortized cost, year five, originated four years before current fiscal year	27,631	1,710
Amortized cost, originated more than five years before current fiscal year	1,330	417
Mortgage loans, amortized cost	3,013,733	2,751,261
Residential Mortgage Loans | 30 - 59 days past due
Financing Receivable, Past Due [Line Items]
Amortized cost, year one, originated in current fiscal year	0	39,179
Amortized cost, year two, originated in fiscal year before current fiscal year	16,627	8,238
Amortized cost, year three, originated two years before current fiscal year	2,516	13,073
Amortized cost, year four, originated three years before current fiscal year	4,960	1,960
Amortized cost, year five, originated four years before current fiscal year	57	0
Amortized cost, originated more than five years before current fiscal year	417	0
Mortgage loans, amortized cost	24,577	62,450
Residential Mortgage Loans | 60 - 89 days past due
Financing Receivable, Past Due [Line Items]
Amortized cost, year one, originated in current fiscal year	0	6,668
Amortized cost, year two, originated in fiscal year before current fiscal year	0	7,165
Amortized cost, year three, originated two years before current fiscal year	0	3,034
Amortized cost, year four, originated three years before current fiscal year	0	57
Amortized cost, year five, originated four years before current fiscal year	0	0
Amortized cost, originated more than five years before current fiscal year	0	0
Mortgage loans, amortized cost	0	16,924
Residential Mortgage Loans | Over 90 days past due
Financing Receivable, Past Due [Line Items]
Amortized cost, year one, originated in current fiscal year	0	9,702
Amortized cost, year two, originated in fiscal year before current fiscal year	7,452	14,068
Amortized cost, year three, originated two years before current fiscal year	16,155	6,515
Amortized cost, year four, originated three years before current fiscal year	7,385	1,762
Amortized cost, year five, originated four years before current fiscal year	1,580	2,796
Amortized cost, originated more than five years before current fiscal year	2,795	0
Mortgage loans, amortized cost	$ 35,367	$ 34,843