Fair Values of Financial Instruments (Quantitative Information) (Details) $ in Thousands	Sep. 30, 2020 USD ($) year	Mar. 31, 2020 USD ($)	Dec. 31, 2019 USD ($) year
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivatives, index options	$ 93,367		$ 157,588
Total assets	3,522,634		3,538,129
Contingent consideration on businesses acquired		$ 4,200
Total liabilities	121,753		171,203
Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivatives, index options	93,367		157,588
Total assets	93,367		157,588
Contingent consideration on businesses acquired	0		4,076
Total liabilities	121,753		171,203
Broker prices | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivatives, index options	93,367		157,588
Deterministic cash flow model | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Policyholder account balances	116,802		155,902
Black-Scholes model | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Share based compensation	$ 4,951		11,225
Probabilistic Method | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Contingent consideration on businesses acquired			$ 4,076
Expected volatility | Black-Scholes model | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Share based compensation, measurement input	0.3285		0.2219
Discount rate | Probabilistic Method | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Contingent consideration on businesses acquired, measurement input			0.100
Minimum | Implied volatility | Broker prices | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivatives, index options, measurement input	0.1296		0.1310
Minimum | Projected option cost | Deterministic cash flow model | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Policyholder account balances, measurement input	0.000		0.000
Minimum | Expected term | Black-Scholes model | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Share based compensation, measurement input | year	1.2		1.9
Minimum | Projected renewal premium | Probabilistic Method | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Contingent consideration on businesses acquired, measurement input			57,200
Maximum | Implied volatility | Broker prices | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivatives, index options, measurement input	0.5369		0.1990
Maximum | Projected option cost | Deterministic cash flow model | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Policyholder account balances, measurement input	0.3869		0.1755
Maximum | Expected term | Black-Scholes model | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Share based compensation, measurement input | year	9.1		10
Maximum | Projected renewal premium | Probabilistic Method | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Contingent consideration on businesses acquired, measurement input			82,400
Weighted-Average | Implied volatility | Broker prices | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivatives, index options, measurement input	0.1974		0.1525
Weighted-Average | Projected option cost | Deterministic cash flow model | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Policyholder account balances, measurement input	0.0518		0.0314
Weighted-Average | Projected renewal premium | Probabilistic Method | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Contingent consideration on businesses acquired, measurement input			71,900