Debt - Selected Information about Debt Issues (Details) - USD ($)	Mar. 31, 2023	Dec. 31, 2022
Debt Instrument [Line Items]
Long-term debt, par value, gross	$ 1,815,612,000
Current maturity of long-term debt, par value	165,612,000
Total long-term debt	1,650,000,000
Total short-term debt, par value	515,612,000
Total debt, par value	2,165,612,000
Unamortized discount & issuance costs, noncurrent	(21,684,000)
Unamortized discount & issuance costs, current maturities	(38,000)
Unamortized discount & issuance costs, long-term debt	(21,646,000)
Unamortized discount & issuance costs, current	(1,365,000)
Total debt, unamortized discount & issuance costs,	(23,011,000)
Long-term debt, net, book value	1,793,928,000	$ 1,793,452,000
Current maturity of long-term debt, book value	165,574,000	165,500,000
Long-term debt	1,628,354,000	1,627,952,000
Total short-term debt, book value	514,247,000	449,103,000
Total debt, book value	2,142,601,000	2,077,055,000
Long-term debt, gross, fair value	1,648,918,000
Current maturity of term loan, fair value	164,746,000
Long-term debt, net, fair value	1,484,172,000
Total short-term debt, fair value	513,419,000
Total debt, fair value	1,997,591,000
FHLB borrowings
Debt Instrument [Line Items]
Total short-term debt, par value	45,000,000	0
Unamortized discount & issuance costs, current	0
Total short-term debt, book value	45,000,000	0
Total short-term debt, fair value	45,000,000
Commercial paper
Debt Instrument [Line Items]
Total short-term debt, par value	305,000,000
Unamortized discount & issuance costs, current	(1,327,000)
Total short-term debt, book value	303,673,000	283,603,000
Total short-term debt, fair value	$ 303,673,000
Senior Notes Due 2023
Debt Instrument [Line Items]
Coupon Rate	7.875%
Long-term debt, par value, gross	$ 165,612,000
Unamortized discount & issuance costs, noncurrent	(38,000)
Debt	165,574,000	165,500,000
Long-term debt, gross, fair value	$ 164,746,000
Senior Notes Due 2028
Debt Instrument [Line Items]
Coupon Rate	4.55%
Long-term debt, par value, gross	$ 550,000,000
Unamortized discount & issuance costs, noncurrent	(4,229,000)
Debt	545,771,000	545,601,000
Long-term debt, gross, fair value	$ 546,348,000
Senior Notes Due 2030
Debt Instrument [Line Items]
Coupon Rate	2.15%
Long-term debt, par value, gross	$ 400,000,000
Unamortized discount & issuance costs, noncurrent	(3,668,000)
Debt	396,332,000	396,219,000
Long-term debt, gross, fair value	$ 323,984,000
Senior Notes Due June 15 2032
Debt Instrument [Line Items]
Coupon Rate	4.80%
Long-term debt, par value, gross	$ 250,000,000
Unamortized discount & issuance costs, noncurrent	(4,412,000)
Debt	245,588,000	245,493,000
Long-term debt, gross, fair value	241,275,000
Senior Notes Due June 15 2032 | Consolidation Eliminations | Subsidiaries
Debt Instrument [Line Items]
Long-term debt, net, book value	$ 150,000,000
Junior Subordinated Debentures Due 2057
Debt Instrument [Line Items]
Coupon Rate	5.275%
Long-term debt, par value, gross	$ 125,000,000
Unamortized discount & issuance costs, noncurrent	(1,585,000)
Debt	123,415,000	123,410,000
Long-term debt, gross, fair value	$ 124,265,000
Junior Subordinated Debentures Due 2061
Debt Instrument [Line Items]
Coupon Rate	4.25%
Long-term debt, par value, gross	$ 325,000,000
Unamortized discount & issuance costs, noncurrent	(7,752,000)
Debt	317,248,000	$ 317,229,000
Long-term debt, gross, fair value	$ 248,300,000