Fair Value (Rollforward of Level 3 assets) (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2013		Mar. 31, 2012
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Balance at beginning of period	$ 477,956		$ 97,215
Total gains or (losses) (realized/unrealized) - included in earnings	6,627	[1]	2,412	[1]
Total gains or (losses) (realized/unrealized) - included in other comprehensive income	224		3,364
Purchases, issuances, sales and settlements
Purchases	46,654		0
Issuances	0		0
Sales	0		0
Settlements	(68,859)		(121)
Transfers in and/or out of Level 3	0		0
Balance at end of period	462,602		102,870
Available for sale | Corporate bonds
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Balance at beginning of period	98,404		92,091
Total gains or (losses) (realized/unrealized) - included in earnings	1,492	[1]	2,331	[1]
Total gains or (losses) (realized/unrealized) - included in other comprehensive income	(1,688)		2,273
Purchases, issuances, sales and settlements
Purchases	0		0
Issuances	0		0
Sales	0		0
Settlements	(910)		(40)
Transfers in and/or out of Level 3	0		0
Balance at end of period	97,298		96,655
Available for sale | Other investments
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Balance at beginning of period	184,202		5,124
Total gains or (losses) (realized/unrealized) - included in earnings	4,762	[1]	81	[1]
Total gains or (losses) (realized/unrealized) - included in other comprehensive income	1,912		1,091
Purchases, issuances, sales and settlements
Purchases	5,000		0
Issuances	0		0
Sales	0		0
Settlements	(9,942)		(81)
Transfers in and/or out of Level 3	0		0
Balance at end of period	185,934		6,215
Fair value option
Fair Value, Assets Measured on Recurring Basis, Unobservable Input Reconciliation [Line Items]
Balance at beginning of period	195,350		0
Total gains or (losses) (realized/unrealized) - included in earnings	373	[1]	0	[1]
Total gains or (losses) (realized/unrealized) - included in other comprehensive income	0		0
Purchases, issuances, sales and settlements
Purchases	41,654		0
Issuances	0		0
Sales	0		0
Settlements	(58,007)		0
Transfers in and/or out of Level 3	0		0
Balance at end of period	$ 179,370		$ 0

[1] Gains or losses on corporate bonds were included in net realized gains (losses) while gains or losses on other investments were recorded in net realized gains (losses) or net investment income.