Fair Value Measurements - Financial instruments not carried at fair value (Details) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2013	Dec. 31, 2012
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fixed maturities, held to maturity	$ 2,802,111	$ 2,814,447
Other investments - structured transactions	293,900	312,100
Deposit liabilities	1,505,180	1,551,398
Notes payable and debt	1,671,062	1,672,778
Fair value of held to maturity securities	3,116,940	3,262,804
Carrying Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fixed maturities, held to maturity	2,802,111	2,814,447
Other investments - structured transactions	293,898	312,122
Financial Assets	3,096,009	3,126,569
Deposit liabilities	1,505,180	1,551,398
Notes payable and debt	1,671,062	1,672,778
Financial Liabilities	3,176,242	3,224,176
Fair Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Fixed maturities, held to maturity	3,116,940	3,262,804
Other investments - structured transactions	291,924	293,813
Financial Assets	3,408,864	3,556,617
Deposit liabilities	1,755,877	1,878,499
Notes payable and debt	1,842,597	1,918,134
Financial Liabilities	$ 3,598,474	$ 3,796,633