Fair Value of Financial Instruments (Fair Value Measurements for Level 3 Instruments) (Details) (USD $) In Thousands, unless otherwise specified	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013
Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Beginning balance	$ 169,314	$ 0
Total realized and unrealized gains (losses):
Included in net income	68,616	0
Included in other comprehensive income (loss)	0	0
Purchases	73,937	0
Sales	0	0
Issuances	0	0
Settlements	(197,580)	0
Transfers into (out of) Level 3	0	169,314
Balance at end of period	114,287	169,314
Change in unrealized gains or losses for the period included in earnings (or changes in net assets) for assets held at the end of the reporting period:	40,350	107,897
Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Beginning balance	193,338	2,718
Total realized and unrealized gains (losses):
Included in net income	73,851	5,725
Included in comprehensive income (loss)	0	0
Purchases	73,937	0
Sales	0	0
Issuances	0	0
Settlements	(198,634)	(2,504)
Transfers into (out of) Level 3	0	187,399
Balance at end of period	142,492	193,338
Change in unrealized gains or losses for the period included in earnings (or changes in net assets) for assets held at the end of the reporting period:	44,722	5,725
Debt Securities, Available for Sale [Member]
Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Beginning balance	0	0
Total realized and unrealized gains (losses):
Included in net income	0	0
Included in other comprehensive income (loss)	0	0
Purchases	0	0
Sales	0	0
Issuances	0	0
Settlements	0	0
Transfers into (out of) Level 3	0	0
Balance at end of period	0	0
Change in unrealized gains or losses for the period included in earnings (or changes in net assets) for assets held at the end of the reporting period:	0	0
Equity Securities, Available for Sale [Member]
Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Beginning balance	0	0
Total realized and unrealized gains (losses):
Included in net income	0	0
Included in other comprehensive income (loss)	0	0
Purchases	0	0
Sales	0	0
Issuances	0	0
Settlements	0	0
Transfers into (out of) Level 3	0	0
Balance at end of period	0	0
Change in unrealized gains or losses for the period included in earnings (or changes in net assets) for assets held at the end of the reporting period:	0	0
Derivatives, Index Options [Member]
Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Beginning balance	169,314	0
Total realized and unrealized gains (losses):
Included in net income	68,616	0
Included in other comprehensive income (loss)	0	0
Purchases	73,937	0
Sales	0	0
Issuances	0	0
Settlements	(197,580)	0
Transfers into (out of) Level 3	0	169,314
Balance at end of period	114,287	169,314
Change in unrealized gains or losses for the period included in earnings (or changes in net assets) for assets held at the end of the reporting period:	40,350	107,897
Net Investment Income [Member]
Total realized and unrealized gains (losses):
Change in unrealized gains or losses for the period included in earnings (or changes in net assets) for assets held at the end of the reporting period:	40,350	107,897
Total realized and unrealized gains (losses):
Change in unrealized gains or losses for the period included in earnings (or changes in net assets) for assets held at the end of the reporting period:	0	5,725
Net Investment Income [Member] | Debt Securities, Available for Sale [Member]
Total realized and unrealized gains (losses):
Change in unrealized gains or losses for the period included in earnings (or changes in net assets) for assets held at the end of the reporting period:	0	0
Net Investment Income [Member] | Equity Securities, Available for Sale [Member]
Total realized and unrealized gains (losses):
Change in unrealized gains or losses for the period included in earnings (or changes in net assets) for assets held at the end of the reporting period:	0	0
Net Investment Income [Member] | Derivatives, Index Options [Member]
Total realized and unrealized gains (losses):
Change in unrealized gains or losses for the period included in earnings (or changes in net assets) for assets held at the end of the reporting period:	40,350	107,897
Other Operating Expense [Member]
Total realized and unrealized gains (losses):
Change in unrealized gains or losses for the period included in earnings (or changes in net assets) for assets held at the end of the reporting period:	0	0
Total realized and unrealized gains (losses):
Change in unrealized gains or losses for the period included in earnings (or changes in net assets) for assets held at the end of the reporting period:	44,722	0
Other Operating Expense [Member] | Debt Securities, Available for Sale [Member]
Total realized and unrealized gains (losses):
Change in unrealized gains or losses for the period included in earnings (or changes in net assets) for assets held at the end of the reporting period:	0	0
Other Operating Expense [Member] | Equity Securities, Available for Sale [Member]
Total realized and unrealized gains (losses):
Change in unrealized gains or losses for the period included in earnings (or changes in net assets) for assets held at the end of the reporting period:	0	0
Other Operating Expense [Member] | Derivatives, Index Options [Member]
Total realized and unrealized gains (losses):
Change in unrealized gains or losses for the period included in earnings (or changes in net assets) for assets held at the end of the reporting period:	$ 0	$ 0