Fair Value of Financial Instruments (Details) (USD $) In Thousands, unless otherwise specified	Dec. 31, 2013		Dec. 31, 2012
U.S. government and federally sponsored agency obligations
Investments, Carrying Value	$ 6,539,473		$ 6,292,097
Separate Account (variable annuity) assets, Carrying Value	1,747,995		1,398,281
Recurring [Member]
U.S. government and federally sponsored agency obligations
Carrying Amount	6,009,573		5,962,232
Fair Value	6,009,573		5,962,232
Investments, Carrying Value	6,313,189		6,103,296
Investments, Fair Value	6,313,189		6,103,296
Separate Account (variable annuity) assets, Carrying Value	1,747,995	[1]	1,398,281	[1]
Separate Account (variable annuity) assets, Fair Value	1,747,995	[1]	1,398,281	[1]
Financial Liabilities	0		0
Recurring [Member] | Other Investments [Member]
U.S. government and federally sponsored agency obligations
Investments, Carrying Value	5,000
Investments, Fair Value	5,000
Short-term investments [Member] | Recurring [Member]
U.S. government and federally sponsored agency obligations
Investments, Carrying Value	206,758		87,561
Investments, Fair Value	206,758		87,561
Mortgage-backed securities [Member] | Recurring [Member]
U.S. government and federally sponsored agency obligations
Carrying Amount	569,725		619,559
Fair Value	569,725		619,559
Other including U.S. Treasury Securities [Member] | Recurring [Member]
U.S. government and federally sponsored agency obligations
Carrying Amount	435,574		409,428
Fair Value	435,574		409,428
Municipal Bonds [Member] | Recurring [Member]
U.S. government and federally sponsored agency obligations
Carrying Amount	1,471,527		1,586,037
Fair Value	1,471,527		1,586,037
Foreign government bonds [Member] | Recurring [Member]
U.S. government and federally sponsored agency obligations
Carrying Amount	54,951		57,869
Fair Value	54,951		57,869
Corporate Bonds [Member] | Recurring [Member]
U.S. government and federally sponsored agency obligations
Carrying Amount	2,614,409		2,567,034
Fair Value	2,614,409		2,567,034
Other Mortgage-backed Securities [Member] | Recurring [Member]
U.S. government and federally sponsored agency obligations
Carrying Amount	863,387		722,305
Fair Value	863,387		722,305
Equity Securities [Member] | Recurring [Member]
U.S. government and federally sponsored agency obligations
Carrying Amount	91,858		53,503
Fair Value	91,858		53,503
Level 1 [Member] | Recurring [Member]
U.S. government and federally sponsored agency obligations
Carrying Amount	27,938		30,528
Investments, Carrying Value	308,571		161,793
Separate Account (variable annuity) assets, Carrying Value	1,747,995	[1]	1,398,281	[1]
Financial Liabilities	0		0
Level 1 [Member] | Recurring [Member] | Other Investments [Member]
U.S. government and federally sponsored agency obligations
Investments, Carrying Value	0
Level 1 [Member] | Short-term investments [Member] | Recurring [Member]
U.S. government and federally sponsored agency obligations
Investments, Carrying Value	206,354		87,561
Level 1 [Member] | Mortgage-backed securities [Member] | Recurring [Member]
U.S. government and federally sponsored agency obligations
Carrying Amount	0		0
Level 1 [Member] | Other including U.S. Treasury Securities [Member] | Recurring [Member]
U.S. government and federally sponsored agency obligations
Carrying Amount	17,757		18,594
Level 1 [Member] | Municipal Bonds [Member] | Recurring [Member]
U.S. government and federally sponsored agency obligations
Carrying Amount	0		0
Level 1 [Member] | Foreign government bonds [Member] | Recurring [Member]
U.S. government and federally sponsored agency obligations
Carrying Amount	0		0
Level 1 [Member] | Corporate Bonds [Member] | Recurring [Member]
U.S. government and federally sponsored agency obligations
Carrying Amount	10,181		11,934
Level 1 [Member] | Other Mortgage-backed Securities [Member] | Recurring [Member]
U.S. government and federally sponsored agency obligations
Carrying Amount	0		0
Level 1 [Member] | Equity Securities [Member] | Recurring [Member]
U.S. government and federally sponsored agency obligations
Carrying Amount	74,279		43,704
Level 2 [Member] | Recurring [Member]
U.S. government and federally sponsored agency obligations
Carrying Amount	5,872,106		5,800,535
Investments, Carrying Value	5,895,083		5,809,994
Separate Account (variable annuity) assets, Carrying Value	0	[1]	0	[1]
Financial Liabilities	0		0
Level 2 [Member] | Recurring [Member] | Other Investments [Member]
U.S. government and federally sponsored agency obligations
Investments, Carrying Value	5,000
Level 2 [Member] | Short-term investments [Member] | Recurring [Member]
U.S. government and federally sponsored agency obligations
Investments, Carrying Value	404		0
Level 2 [Member] | Mortgage-backed securities [Member] | Recurring [Member]
U.S. government and federally sponsored agency obligations
Carrying Amount	569,725		619,559
Level 2 [Member] | Other including U.S. Treasury Securities [Member] | Recurring [Member]
U.S. government and federally sponsored agency obligations
Carrying Amount	417,817		390,834
Level 2 [Member] | Municipal Bonds [Member] | Recurring [Member]
U.S. government and federally sponsored agency obligations
Carrying Amount	1,468,833		1,573,762
Level 2 [Member] | Foreign government bonds [Member] | Recurring [Member]
U.S. government and federally sponsored agency obligations
Carrying Amount	54,951		57,869
Level 2 [Member] | Corporate Bonds [Member] | Recurring [Member]
U.S. government and federally sponsored agency obligations
Carrying Amount	2,543,402		2,469,378
Level 2 [Member] | Other Mortgage-backed Securities [Member] | Recurring [Member]
U.S. government and federally sponsored agency obligations
Carrying Amount	817,378		689,133
Level 2 [Member] | Equity Securities [Member] | Recurring [Member]
U.S. government and federally sponsored agency obligations
Carrying Amount	17,573		9,459
Level 3 [Member] | Recurring [Member]
U.S. government and federally sponsored agency obligations
Carrying Amount	109,529		131,169
Investments, Carrying Value	109,535		131,509
Separate Account (variable annuity) assets, Carrying Value	0	[1]	0	[1]
Financial Liabilities	0		0
Level 3 [Member] | Recurring [Member] | Other Investments [Member]
U.S. government and federally sponsored agency obligations
Investments, Carrying Value	0
Level 3 [Member] | Short-term investments [Member] | Recurring [Member]
U.S. government and federally sponsored agency obligations
Investments, Carrying Value	0		0
Level 3 [Member] | Mortgage-backed securities [Member] | Recurring [Member]
U.S. government and federally sponsored agency obligations
Carrying Amount	0		0
Level 3 [Member] | Other including U.S. Treasury Securities [Member] | Recurring [Member]
U.S. government and federally sponsored agency obligations
Carrying Amount	0		0
Level 3 [Member] | Municipal Bonds [Member] | Recurring [Member]
U.S. government and federally sponsored agency obligations
Carrying Amount	2,694		12,275
Level 3 [Member] | Foreign government bonds [Member] | Recurring [Member]
U.S. government and federally sponsored agency obligations
Carrying Amount	0		0
Level 3 [Member] | Corporate Bonds [Member] | Recurring [Member]
U.S. government and federally sponsored agency obligations
Carrying Amount	60,826		85,722
Level 3 [Member] | Other Mortgage-backed Securities [Member] | Recurring [Member]
U.S. government and federally sponsored agency obligations
Carrying Amount	46,009		33,172
Level 3 [Member] | Equity Securities [Member] | Recurring [Member]
U.S. government and federally sponsored agency obligations
Carrying Amount	$ 6		$ 340

[1] Separate Account (variable annuity) liabilities are set equal to Separate Account (variable annuity) assets.