Fair Values of Financial Instruments (Quantitative Information) (Details) - USD ($) $ in Thousands	Mar. 31, 2018	Dec. 31, 2017
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, fair value disclosure	$ 3,219,318	$ 3,254,340
Liabilities, fair value disclosure	147,502	226,401
Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, fair value disclosure	116,356	194,731
Liabilities, fair value disclosure	147,502	226,401
Derivatives, index options | Broker prices | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets, fair value disclosure	116,356	194,731
Policyholder account balances | Deterministic cash flow model | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Liabilities, fair value disclosure	134,293	211,159
Other liabilities | Black-Scholes model | Level 3
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Liabilities, fair value disclosure	$ 13,209	$ 15,242