Investments (Credit Quality Indicators) (Details) - USD ($) $ in Thousands	Jun. 30, 2021	Dec. 31, 2020
Financing Receivable, Credit Quality Indicator [Line Items]
Recording investment gross of allowance for credit losses	$ 2,159,318	$ 1,773,152
Commercial Mortgage Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Current Year	284,139	256,178
One Years Prior	255,776	370,081
Two Years Prior	414,467	107,164
Three Years Prior	105,950	287,341
Four Years Prior	308,547	289,478
Prior	684,646	358,336
Recording investment gross of allowance for credit losses	2,053,525	1,668,578
Commercial Mortgage Loans | ≥ 1.2X
Financing Receivable, Credit Quality Indicator [Line Items]
Current Year	284,139	256,178
One Years Prior	255,776	347,151
Two Years Prior	391,833	107,164
Three Years Prior	105,950	287,341
Four Years Prior	296,139	274,124
Prior	635,450	323,060
Recording investment gross of allowance for credit losses	1,969,287	1,595,018
Commercial Mortgage Loans | 1.0X to 1.2X
Financing Receivable, Credit Quality Indicator [Line Items]
Current Year	0	0
One Years Prior	0	22,930
Two Years Prior	22,634	0
Three Years Prior	0	0
Four Years Prior	12,408	3,969
Prior	21,483	18,420
Recording investment gross of allowance for credit losses	56,525	45,319
Commercial Mortgage Loans | Less than 1.0X
Financing Receivable, Credit Quality Indicator [Line Items]
Current Year	0	0
One Years Prior	0	0
Two Years Prior	0	0
Three Years Prior	0	0
Four Years Prior	0	11,385
Prior	27,713	16,856
Recording investment gross of allowance for credit losses	27,713	28,241
Agricultural Property Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Current Year	8,135	49,507
One Years Prior	49,323	13,769
Two Years Prior	13,741	1,255
Three Years Prior	1,244	7,493
Four Years Prior	2,708	1,180
Prior	30,642	31,370
Recording investment gross of allowance for credit losses	105,793	104,574
Agricultural Property Loans | ≥ 1.2X
Financing Receivable, Credit Quality Indicator [Line Items]
Current Year	8,135	49,507
One Years Prior	49,323	13,769
Two Years Prior	13,741	1,255
Three Years Prior	1,244	4,277
Four Years Prior	2,708	1,180
Prior	27,203	27,783
Recording investment gross of allowance for credit losses	102,354	97,771
Agricultural Property Loans | 1.0X to 1.2X
Financing Receivable, Credit Quality Indicator [Line Items]
Current Year	0	0
One Years Prior	0	0
Two Years Prior	0	0
Three Years Prior	0	0
Four Years Prior	0	0
Prior	0	0
Recording investment gross of allowance for credit losses	0	0
Agricultural Property Loans | Less than 1.0X
Financing Receivable, Credit Quality Indicator [Line Items]
Current Year	0	0
One Years Prior	0	0
Two Years Prior	0	0
Three Years Prior	0	3,216
Four Years Prior	0	0
Prior	3,439	3,587
Recording investment gross of allowance for credit losses	3,439	6,803
0%-59.99% | Commercial Mortgage Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Current Year	72,985	0
One Years Prior	3,800	114,636
Two Years Prior	131,266	36,423
Three Years Prior	42,789	116,130
Four Years Prior	119,973	175,740
Prior	469,790	255,848
Recording investment gross of allowance for credit losses	840,603	698,777
0%-59.99% | Agricultural Property Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Current Year	8,135	47,245
One Years Prior	47,138	13,769
Two Years Prior	13,741	1,255
Three Years Prior	1,244	7,493
Four Years Prior	2,708	1,180
Prior	30,642	31,370
Recording investment gross of allowance for credit losses	103,608	102,312
60%-69.99% | Commercial Mortgage Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Current Year	99,026	174,507
One Years Prior	171,906	204,112
Two Years Prior	232,198	59,935
Three Years Prior	52,478	90,954
Four Years Prior	134,709	57,569
Prior	121,830	54,530
Recording investment gross of allowance for credit losses	812,147	641,607
60%-69.99% | Agricultural Property Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Current Year	0	2,262
One Years Prior	2,185	0
Two Years Prior	0	0
Three Years Prior	0	0
Four Years Prior	0	0
Prior	0	0
Recording investment gross of allowance for credit losses	2,185	2,262
70%-79.99% | Commercial Mortgage Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Current Year	112,128	81,671
One Years Prior	80,070	51,333
Two Years Prior	51,003	10,806
Three Years Prior	10,683	80,257
Four Years Prior	53,865	56,169
Prior	91,936	46,855
Recording investment gross of allowance for credit losses	399,685	327,091
70%-79.99% | Agricultural Property Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Current Year	0	0
One Years Prior	0	0
Two Years Prior	0	0
Three Years Prior	0	0
Four Years Prior	0	0
Prior	0	0
Recording investment gross of allowance for credit losses	0	0
80% or greater | Commercial Mortgage Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Current Year	0	0
One Years Prior	0	0
Two Years Prior	0	0
Three Years Prior	0	0
Four Years Prior	0	0
Prior	1,090	1,103
Recording investment gross of allowance for credit losses	1,090	1,103
80% or greater | Agricultural Property Loans
Financing Receivable, Credit Quality Indicator [Line Items]
Current Year	0	0
One Years Prior	0	0
Two Years Prior	0	0
Three Years Prior	0	0
Four Years Prior	0	0
Prior	0	0
Recording investment gross of allowance for credit losses	$ 0	$ 0