Fair Value of Financial Instruments (Fair Value Measurements for Level 3 Instruments) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		12 Months Ended
	Mar. 31, 2015	Mar. 31, 2014	Dec. 31, 2014
Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Balance at January 1, 2014	$ 114,287	$ 169,314	$ 169,314
Total realized and unrealized gains (losses):
Included in net income	(8,287)		548
Included in other comprehensive income	0		0
Purchases	18,456	15,337
Sales	0	0
Issuances	0	0
Settlements	(28,469)	(50,283)
Transfers into (out of) Level 3	0		0
Balance at end of period	95,987	134,916	114,287
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:	(6,843)	2,821
Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Balance at January 1, 2014	142,492	193,338	193,338
Total realized and unrealized gains (losses):
Included in net income	(12,383)		2,651
Included in other comprehensive income	0		0
Purchases	18,456	15,337
Sales	0	0
Issuances	0	0
Settlements	28,578	50,790
Transfers into (out of) Level 3	0		0
Balance at end of period	119,987	160,536	142,492
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:	(787)	1,667
Debt Securities, Available for Sale [Member]
Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Balance at January 1, 2014	0	0	0
Total realized and unrealized gains (losses):
Included in net income	0		0
Included in other comprehensive income	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	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]
Balance at January 1, 2014	0	0	0
Total realized and unrealized gains (losses):
Included in net income	0		0
Included in other comprehensive income	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	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]
Balance at January 1, 2014	114,287	169,314	169,314
Total realized and unrealized gains (losses):
Included in net income	(8,287)		548
Included in other comprehensive income	0		0
Purchases	18,456	15,337
Sales	0	0
Issuances	0	0
Settlements	(28,469)	(50,283)
Transfers into (out of) Level 3	0		0
Balance at end of period	95,987	134,916	114,287
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:	(6,843)	2,821
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:	(6,843)	2,821
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] | 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:	(6,843)	2,821
Other Operating Income (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:	(787)	1,667
Other Operating Income (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 Income (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 Income (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