Fair Value of Financial Instruments (Quantitative Information About Level 3 Fair Value Measurements) (Details) $ in Thousands	Sep. 30, 2020 USD ($)	Dec. 31, 2019 USD ($)
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Available-for-sale securities	$ 1,717,039	$ 1,719,607
Nonredeemable preferred stocks	198,791	299,203
Asset-backed securities
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Available-for-sale securities		750
Financial services | Corporate bonds
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Available-for-sale securities		100,253
Recurring
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Available-for-sale securities	1,717,047	1,719,607
Nonredeemable preferred stocks	198,791	299,203
Recurring | Asset-backed securities
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Available-for-sale securities	935	750
Recurring | Nonredeemable preferred stocks
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Nonredeemable preferred stocks	6,641	6,674
Recurring | Financial services
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Nonredeemable preferred stocks	63,957	127,780
Recurring | Financial services | Corporate bonds
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Available-for-sale securities	102,459	100,253
Recurring | Level 3
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Available-for-sale securities	1,185	1,000
Nonredeemable preferred stocks	595	595
Recurring | Level 3 | Asset-backed securities
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Available-for-sale securities	$ 935	750
Recurring | Level 3 | Asset-backed securities | Discounted cash flow | Minimum
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Available-for-sale securities, range of weighted average significant unobservable inputs	0.04
Recurring | Level 3 | Asset-backed securities | Discounted cash flow | Maximum
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Available-for-sale securities, range of weighted average significant unobservable inputs	0.06
Recurring | Level 3 | Nonredeemable preferred stocks
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Nonredeemable preferred stocks	$ 595	595
Recurring | Level 3 | Nonredeemable preferred stocks | Discounted cash flow | Minimum
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Nonredeemable preferred stocks, range of weighted average significant unobservable inputs	0.03
Recurring | Level 3 | Nonredeemable preferred stocks | Discounted cash flow | Maximum
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Nonredeemable preferred stocks, range of weighted average significant unobservable inputs	0.04
Recurring | Level 3 | Financial services
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Nonredeemable preferred stocks	$ 0	0
Recurring | Level 3 | Financial services | Corporate bonds
Fair Value Measurement Inputs and Valuation Techniques [Line Items]
Available-for-sale securities	$ 250	$ 250