Fair Value of Financial Instruments (Assets and Liabilities Measured on Recurring Basis) (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2015		Dec. 31, 2014
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale, at fair value (cost: $2,687,568 and $2,590,074)	$ 2,854,690		$ 2,728,680
Derivatives, index options	95,987		114,287
Total assets	2,950,677		2,842,967
Policyholder account balances	111,627	[1]	133,236	[1]
Other liabilities	8,360	[2]	9,256	[2]
Total liabilities	119,987		142,492
Percent of total	100.00%		100.00%
Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale, at fair value (cost: $2,687,568 and $2,590,074)	17,059		16,862
Derivatives, index options	0		0
Total assets	17,059		16,862
Policyholder account balances	0		0
Other liabilities	0		0
Total liabilities	0		0
Percent of total	0.60%		0.60%
Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale, at fair value (cost: $2,687,568 and $2,590,074)	2,837,631		2,711,818
Derivatives, index options	0		0
Total assets	2,837,631		2,711,818
Policyholder account balances
Other liabilities	0		0
Total liabilities	0		0
Percent of total	96.10%		95.40%
Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale, at fair value (cost: $2,687,568 and $2,590,074)	0		0
Derivatives, index options	95,987		114,287
Total assets	95,987		114,287
Policyholder account balances	111,627		133,236
Other liabilities	8,360		9,256
Total liabilities	119,987		142,492
Percent of total	3.30%		4.00%
Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale, at fair value (cost: $2,687,568 and $2,590,074)	2,837,075		2,711,377
Debt Securities [Member] | Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale, at fair value (cost: $2,687,568 and $2,590,074)	0		0
Debt Securities [Member] | Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale, at fair value (cost: $2,687,568 and $2,590,074)	2,837,075		2,711,377
Debt Securities [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale, at fair value (cost: $2,687,568 and $2,590,074)	0		0
Equity Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale, at fair value (cost: $2,687,568 and $2,590,074)	17,615		17,303
Equity Securities [Member] | Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale, at fair value (cost: $2,687,568 and $2,590,074)	17,059		16,862
Equity Securities [Member] | Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale, at fair value (cost: $2,687,568 and $2,590,074)	556		441
Equity Securities [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale, at fair value (cost: $2,687,568 and $2,590,074)	0		0
Derivatives, Index Options [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivatives, index options	95,987		114,287
Derivatives, Index Options [Member] | Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivatives, index options	0		0
Derivatives, Index Options [Member] | Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivatives, index options	0		0
Derivatives, Index Options [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivatives, index options	95,987		114,287
Priced by Third-Party Vendors [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivatives, index options	95,987		114,287
Priced by Third-Party Vendors [Member] | Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivatives, index options	0		0
Priced by Third-Party Vendors [Member] | Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivatives, index options	0		0
Priced by Third-Party Vendors [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivatives, index options	95,987		114,287
Priced by Third-Party Vendors [Member] | Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale, at fair value (cost: $2,687,568 and $2,590,074)	2,837,075		2,711,377
Priced by Third-Party Vendors [Member] | Debt Securities [Member] | Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale, at fair value (cost: $2,687,568 and $2,590,074)	0		0
Priced by Third-Party Vendors [Member] | Debt Securities [Member] | Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale, at fair value (cost: $2,687,568 and $2,590,074)	2,837,075		2,711,377
Priced by Third-Party Vendors [Member] | Debt Securities [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale, at fair value (cost: $2,687,568 and $2,590,074)	0		0
Priced by Third-Party Vendors [Member] | Equity Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale, at fair value (cost: $2,687,568 and $2,590,074)	17,615		17,303
Priced by Third-Party Vendors [Member] | Equity Securities [Member] | Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale, at fair value (cost: $2,687,568 and $2,590,074)	17,059		16,862
Priced by Third-Party Vendors [Member] | Equity Securities [Member] | Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale, at fair value (cost: $2,687,568 and $2,590,074)	556		441
Priced by Third-Party Vendors [Member] | Equity Securities [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale, at fair value (cost: $2,687,568 and $2,590,074)	0		0
Priced Internally [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivatives, index options	0		0
Priced Internally [Member] | Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivatives, index options	0		0
Priced Internally [Member] | Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivatives, index options	0		0
Priced Internally [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Derivatives, index options	0		0
Priced Internally [Member] | Debt Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale, at fair value (cost: $2,687,568 and $2,590,074)	0		0
Priced Internally [Member] | Debt Securities [Member] | Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale, at fair value (cost: $2,687,568 and $2,590,074)	0		0
Priced Internally [Member] | Debt Securities [Member] | Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale, at fair value (cost: $2,687,568 and $2,590,074)	0		0
Priced Internally [Member] | Debt Securities [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale, at fair value (cost: $2,687,568 and $2,590,074)	0		0
Priced Internally [Member] | Equity Securities [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale, at fair value (cost: $2,687,568 and $2,590,074)	0		0
Priced Internally [Member] | Equity Securities [Member] | Level 1 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale, at fair value (cost: $2,687,568 and $2,590,074)	0		0
Priced Internally [Member] | Equity Securities [Member] | Level 2 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale, at fair value (cost: $2,687,568 and $2,590,074)	0		0
Priced Internally [Member] | Equity Securities [Member] | Level 3 [Member]
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Securities available for sale, at fair value (cost: $2,687,568 and $2,590,074)	$ 0		$ 0

[1] Represents the fair value of certain product-related embedded derivatives that were recorded at fair value.

[2] Represents the liability for share-based compensation.