Senior Notes, Convertible Notes and Trust Preferred Securities - Schedule of Long-term Debt Instruments (Details) - Senior Notes - USD ($)	Dec. 31, 2020	Dec. 31, 2019
Debt Instrument [Line Items]
Principal amount of debt component	$ 787,688,000	$ 500,000,000
Unamortized debt discounts	(3,491,000)	(963,000)
Unamortized debt issuance costs	(4,922,000)	(2,167,000)
Long-term debt	779,275,000	496,870,000
Senior Notes Due 2030
Debt Instrument [Line Items]
Principal amount of debt component	400,000,000	0
Unamortized debt discounts	$ (3,068,000)
Interest Rate	2.70%
Issue Price	99.233%
Senior Notes Due 2024
Debt Instrument [Line Items]
Principal amount of debt component	$ 198,932,000	250,000,000
Interest Rate	4.40%
Issue Price	99.883%
Senior Notes Due 2023
Debt Instrument [Line Items]
Principal amount of debt component	$ 188,756,000	$ 250,000,000
Interest Rate	4.25%
Issue Price	99.026%

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Amount, after accumulated amortization, of debt discount.

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Amount, after accumulated amortization, of debt issuance costs. Includes, but is not limited to, legal, accounting, underwriting, printing, and registration costs.

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Amount, after unamortized (discount) premium and debt issuance costs, of long-term debt. Includes, but not limited to, notes payable, bonds payable, debentures, mortgage loans and commercial paper. Excludes capital lease obligations.

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