Fair Value of Financial Instruments (Fair Value Measurements for Level 3 Instruments) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Beginning balance	$ 146,514	$ 0	$ 169,314	$ 0
Total realized and unrealized gains (losses):
Included in net income	3,479	0	49,278	0
Included in other comprehensive income	0	0	0	0
Purchases, sales, issuances and settlements, net	(40,181)	0	(108,780)	0
Transfers into (out of) Level 3	0	0	0	0
Balance at end of period	109,812	0	109,812	0
Amount of total gains (losses) for the period included in net income attributable to the change in unrealized gains (losses) relating to assets still held at the end of period	747	0	29,895	0
Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Beginning balance	171,428	4,370	193,338	2,718
Total realized and unrealized gains (losses):
Included in net income	4,099	1,010	51,529	3,976
Included in comprehensive income	0	0	0	0
Purchases, sales, issuances and settlements, net	(40,201)	(827)	109,541	2,141
Transfers into (out of) Level 3	0	0	0	0
Balance at end of period	135,326	4,553	135,326	4,553
Fair Value, Liabilities Measured on Recurring Basis, Change in Unrealized Gain (Loss)	175	1,601	3,266	5,343
Debt Securities, Available for Sale [Member]
Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Beginning balance	0	0	0	0
Total realized and unrealized gains (losses):
Included in net income	0	0	0	0
Included in other comprehensive income	0	0	0	0
Purchases, sales, issuances and settlements, net		0	0	0
Transfers into (out of) Level 3	0	0	0	0
Balance at end of period	0	0	0	0
Amount of total gains (losses) for the period included in net income attributable to the change in unrealized gains (losses) relating to assets still held at the end of period	0	0	0	0
Equity Securities, Available for Sale [Member]
Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Beginning balance	0	0	0	0
Total realized and unrealized gains (losses):
Included in net income	0	0	0	0
Included in other comprehensive income	0	0	0	0
Purchases, sales, issuances and settlements, net		0	0	0
Transfers into (out of) Level 3	0	0	0	0
Balance at end of period	0	0	0	0
Amount of total gains (losses) for the period included in net income attributable to the change in unrealized gains (losses) relating to assets still held at the end of period	0	0	0	0
Derivatives, Index Options [Member]
Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Roll Forward]
Beginning balance	146,514	0	169,314	0
Total realized and unrealized gains (losses):
Included in net income	3,479	0	49,278	0
Included in other comprehensive income	0	0	0	0
Purchases, sales, issuances and settlements, net	(40,181)	0	(108,780)	0
Transfers into (out of) Level 3	0	0	0	0
Balance at end of period	109,812	0	109,812	0
Amount of total gains (losses) for the period included in net income attributable to the change in unrealized gains (losses) relating to assets still held at the end of period	747	0	29,895	0
Net Investment Income [Member]
Total realized and unrealized gains (losses):
Amount of total gains (losses) for the period included in net income attributable to the change in unrealized gains (losses) relating to assets still held at the end of period	747	0	29,895	0
Total realized and unrealized gains (losses):
Fair Value, Liabilities Measured on Recurring Basis, Change in Unrealized Gain (Loss)	0	0	0	0
Net Investment Income [Member] | Debt Securities, Available for Sale [Member]
Total realized and unrealized gains (losses):
Amount of total gains (losses) for the period included in net income attributable to the change in unrealized gains (losses) relating to assets still held at the end of period	0	0	0	0
Net Investment Income [Member] | Equity Securities, Available for Sale [Member]
Total realized and unrealized gains (losses):
Amount of total gains (losses) for the period included in net income attributable to the change in unrealized gains (losses) relating to assets still held at the end of period	0	0	0	0
Net Investment Income [Member] | Derivatives, Index Options [Member]
Total realized and unrealized gains (losses):
Amount of total gains (losses) for the period included in net income attributable to the change in unrealized gains (losses) relating to assets still held at the end of period	747	0	29,895	0
Other Operating Income (Expense) [Member]
Total realized and unrealized gains (losses):
Amount of total gains (losses) for the period included in net income attributable to the change in unrealized gains (losses) relating to assets still held at the end of period	0	0	0	0
Total realized and unrealized gains (losses):
Fair Value, Liabilities Measured on Recurring Basis, Change in Unrealized Gain (Loss)	175	1,601	3,266	5,343
Other Operating Income (Expense) [Member] | Debt Securities, Available for Sale [Member]
Total realized and unrealized gains (losses):
Amount of total gains (losses) for the period included in net income attributable to the change in unrealized gains (losses) relating to assets still held at the end of period	0	0	0	0
Other Operating Income (Expense) [Member] | Equity Securities, Available for Sale [Member]
Total realized and unrealized gains (losses):
Amount of total gains (losses) for the period included in net income attributable to the change in unrealized gains (losses) relating to assets still held at the end of period	0	0	0	0
Other Operating Income (Expense) [Member] | Derivatives, Index Options [Member]
Total realized and unrealized gains (losses):
Amount of total gains (losses) for the period included in net income attributable to the change in unrealized gains (losses) relating to assets still held at the end of period	$ 0	$ 0	$ 0	$ 0