Fair Value of Financial Instruments - Assets and Liabilities Carrying at Fair Value Measured on a Recurring Basis (Details) (USD $) | Dec. 31, 2013 | Sep. 30, 2013 |
In Thousands, unless otherwise specified |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | ' |
Derivative investments | $294,531 | $221,758 |
Assets, Fair Value Disclosure | 1,097,925 | 870,276 |
Level 1 | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | ' |
Cash and Cash Equivalents, Fair Value Disclosure | 759,471 | 1,204,334 |
Equity securities - available-for-sale | 0 | 0 |
Derivative investments | 0 | 0 |
Related Party Loans and Investments, Fair Value | 0 | 0 |
Other Assets, Fair Value Disclosure | 0 | 0 |
Assets, Fair Value Disclosure | 1,262,002 | 1,995,260 |
Liabilities Related to Investment Contracts, Fair Value Disclosure | 0 | 0 |
Other Liabilities, Fair Value Disclosure | ' | 0 |
Debt Instrument, Fair Value Disclosure | 0 | 0 |
Financial Liabilities Fair Value Disclosure | 0 | 0 |
Level 2 | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | ' |
Cash and Cash Equivalents, Fair Value Disclosure | 0 | 0 |
Equity securities - available-for-sale | 286,922 | 271,075 |
Derivative investments | 294,531 | 221,758 |
Related Party Loans and Investments, Fair Value | 0 | 0 |
Other Assets, Fair Value Disclosure | 0 | 0 |
Assets, Fair Value Disclosure | 15,621,960 | 14,648,182 |
Liabilities Related to Investment Contracts, Fair Value Disclosure | 0 | 0 |
Other Liabilities, Fair Value Disclosure | ' | 22,833 |
Debt Instrument, Fair Value Disclosure | 300,000 | 300,000 |
Financial Liabilities Fair Value Disclosure | 328,328 | 323,861 |
Level 3 | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | ' |
Cash and Cash Equivalents, Fair Value Disclosure | 0 | 0 |
Equity securities - available-for-sale | 0 | 0 |
Derivative investments | 0 | 0 |
Related Party Loans and Investments, Fair Value | 96,442 | 119,044 |
Other Assets, Fair Value Disclosure | 316,552 | 188,180 |
Assets, Fair Value Disclosure | 1,311,283 | 1,020,500 |
Liabilities Related to Investment Contracts, Fair Value Disclosure | 12,513,803 | 12,378,645 |
Other Liabilities, Fair Value Disclosure | ' | 0 |
Debt Instrument, Fair Value Disclosure | 0 | 0 |
Financial Liabilities Fair Value Disclosure | 14,158,527 | 13,923,092 |
Fair Value | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | ' |
Cash and Cash Equivalents, Fair Value Disclosure | 759,471 | 1,204,334 |
Equity securities - available-for-sale | 286,922 | 271,075 |
Derivative investments | 294,531 | 221,758 |
Related Party Loans and Investments, Fair Value | 96,442 | 119,044 |
Other Assets, Fair Value Disclosure | 316,552 | 188,180 |
Assets, Fair Value Disclosure | 18,195,245 | 17,663,942 |
Liabilities Related to Investment Contracts, Fair Value Disclosure | 12,513,803 | 12,378,645 |
Other Liabilities, Fair Value Disclosure | ' | 22,833 |
Debt Instrument, Fair Value Disclosure | 300,000 | 300,000 |
Financial Liabilities Fair Value Disclosure | 14,486,855 | 14,246,953 |
Carrying Value | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | ' |
Cash and Cash Equivalents, Fair Value Disclosure | 759,471 | 1,204,334 |
Equity securities - available-for-sale | 286,922 | 271,075 |
Derivative investments | 294,531 | 221,758 |
Related Party Loans and Investments, Fair Value | 96,442 | 119,044 |
Other Assets, Fair Value Disclosure | 316,552 | 188,180 |
Assets, Fair Value Disclosure | 18,195,245 | 17,663,942 |
Liabilities Related to Investment Contracts, Fair Value Disclosure | 13,874,998 | 13,703,769 |
Other Liabilities, Fair Value Disclosure | ' | 22,833 |
Debt Instrument, Fair Value Disclosure | 300,000 | 300,000 |
Financial Liabilities Fair Value Disclosure | 15,848,050 | 15,572,077 |
Embedded derivatives in Reinsurance contracts | Level 1 | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | ' |
Derivative investments | 0 | 0 |
Embedded derivatives in Reinsurance contracts | Level 2 | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | ' |
Derivative investments | 113,710 | 118,025 |
Embedded derivatives in Reinsurance contracts | Level 3 | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | ' |
Derivative investments | 0 | 0 |
Embedded derivatives in Reinsurance contracts | Fair Value | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | ' |
Derivative investments | 113,710 | 118,025 |
Embedded derivatives in Reinsurance contracts | Carrying Value | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | ' |
Derivative investments | 113,710 | 118,025 |
Fixed Index Annuity | Level 1 | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | ' |
Derivative Liability | 0 | 0 |
Fixed Index Annuity | Level 2 | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | ' |
Derivative Liability | 0 | 0 |
Fixed Index Annuity | Level 3 | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | ' |
Derivative Liability | 1,644,724 | 1,544,447 |
Fixed Index Annuity | Fair Value | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | ' |
Derivative Liability | 1,644,724 | 1,544,447 |
Fixed Index Annuity | Carrying Value | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | ' |
Derivative Liability | 1,644,724 | 1,544,447 |
Future Contracts | Level 1 | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | ' |
Derivative Liability | ' | 0 |
Future Contracts | Level 2 | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | ' |
Derivative Liability | ' | 1,028 |
Future Contracts | Level 3 | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | ' |
Derivative Liability | ' | 0 |
Future Contracts | Fair Value | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | ' |
Derivative Liability | ' | 1,028 |
Future Contracts | Carrying Value | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | ' |
Derivative Liability | ' | 1,028 |
Call options | Level 1 | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | ' |
Other Liabilities, Fair Value Disclosure | 0 | ' |
Call options | Level 2 | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | ' |
Other Liabilities, Fair Value Disclosure | 28,328 | ' |
Call options | Level 3 | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | ' |
Other Liabilities, Fair Value Disclosure | 0 | ' |
Call options | Fair Value | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | ' |
Other Liabilities, Fair Value Disclosure | 28,328 | ' |
Call options | Carrying Value | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | ' |
Other Liabilities, Fair Value Disclosure | 28,328 | ' |
Asset-backed securities | Level 1 | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | ' |
Available-for-sale Securities | 0 | 0 |
Asset-backed securities | Level 2 | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | ' |
Available-for-sale Securities | 1,591,978 | 1,518,066 |
Asset-backed securities | Level 3 | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | ' |
Available-for-sale Securities | 250,800 | 246,528 |
Asset-backed securities | Fair Value | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | ' |
Available-for-sale Securities | 1,842,778 | 1,764,594 |
Asset-backed securities | Carrying Value | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | ' |
Available-for-sale Securities | 1,842,778 | 1,764,594 |
Commercial mortgage-backed securities | Level 1 | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | ' |
Available-for-sale Securities | 0 | 0 |
Commercial mortgage-backed securities | Level 2 | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | ' |
Available-for-sale Securities | 438,653 | 448,694 |
Commercial mortgage-backed securities | Level 3 | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | ' |
Available-for-sale Securities | 5,976 | 5,635 |
Commercial mortgage-backed securities | Fair Value | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | ' |
Available-for-sale Securities | 444,629 | 454,329 |
Commercial mortgage-backed securities | Carrying Value | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | ' |
Available-for-sale Securities | 444,629 | 454,329 |
Corporates | Level 1 | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | ' |
Available-for-sale Securities | 0 | 0 |
Corporates | Level 2 | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | ' |
Available-for-sale Securities | 9,439,479 | 8,957,196 |
Corporates | Level 3 | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | ' |
Available-for-sale Securities | 607,139 | 461,113 |
Corporates | Fair Value | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | ' |
Available-for-sale Securities | 10,046,618 | 9,418,309 |
Corporates | Carrying Value | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | ' |
Available-for-sale Securities | 10,046,618 | 9,418,309 |
Hybrids | Level 1 | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | ' |
Available-for-sale Securities | 0 | 0 |
Hybrids | Level 2 | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | ' |
Available-for-sale Securities | 418,074 | 428,817 |
Hybrids | Level 3 | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | ' |
Available-for-sale Securities | 0 | 0 |
Hybrids | Fair Value | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | ' |
Available-for-sale Securities | 418,074 | 428,817 |
Hybrids | Carrying Value | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | ' |
Available-for-sale Securities | 418,074 | 428,817 |
Municipals | Level 1 | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | ' |
Available-for-sale Securities | 0 | 0 |
Municipals | Level 2 | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | ' |
Available-for-sale Securities | 1,087,052 | 1,007,010 |
Municipals | Level 3 | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | ' |
Available-for-sale Securities | 34,374 | 0 |
Municipals | Fair Value | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | ' |
Available-for-sale Securities | 1,121,426 | 1,007,010 |
Municipals | Carrying Value | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | ' |
Available-for-sale Securities | 1,121,426 | 1,007,010 |
Residential Mortgage Backed Securities | Level 1 | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | ' |
Available-for-sale Securities | 0 | 0 |
Residential Mortgage Backed Securities | Level 2 | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | ' |
Available-for-sale Securities | 91,049 | 98,597 |
Residential Mortgage Backed Securities | Level 3 | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | ' |
Available-for-sale Securities | 0 | 0 |
Residential Mortgage Backed Securities | Fair Value | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | ' |
Available-for-sale Securities | 91,049 | 98,597 |
Residential Mortgage Backed Securities | Carrying Value | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | ' |
Available-for-sale Securities | 91,049 | 98,597 |
Non-agency residential mortgage-backed securities | Level 1 | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | ' |
Available-for-sale Securities | 0 | 0 |
Non-agency residential mortgage-backed securities | Level 2 | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | ' |
Available-for-sale Securities | 1,652,027 | 1,368,023 |
Non-agency residential mortgage-backed securities | Level 3 | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | ' |
Available-for-sale Securities | 0 | 0 |
Non-agency residential mortgage-backed securities | Fair Value | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | ' |
Available-for-sale Securities | 1,652,027 | 1,368,023 |
Non-agency residential mortgage-backed securities | Carrying Value | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | ' |
Available-for-sale Securities | 1,652,027 | 1,368,023 |
U.S. Government securities | Level 1 | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | ' |
Available-for-sale Securities | 502,531 | 790,926 |
U.S. Government securities | Level 2 | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | ' |
Available-for-sale Securities | 208,485 | 210,921 |
U.S. Government securities | Level 3 | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | ' |
Available-for-sale Securities | 0 | 0 |
U.S. Government securities | Fair Value | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | ' |
Available-for-sale Securities | 711,016 | 1,001,847 |
U.S. Government securities | Carrying Value | ' | ' |
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items] | ' | ' |
Available-for-sale Securities | $711,016 | $1,001,847 |