Other Comprehensive income (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended
	Mar. 31, 2012	Mar. 31, 2011	Dec. 31, 2011
Other comprehensive income (before tax) [Abstract]
Change in unrealized gains and losses on investments	$ (46,926)	$ (25,358)
Unrealized foreign currency translation adjustment	1,667	1,411
Other comprehensive income (loss)	(45,259)	(23,947)
Other comprehensive income (tax) [Abstract]
Change in unrealized gains and losses on investments	16,256	8,916
Unrealized foreign currency translation adjustment	(584)	(494)
Other comprehensive income (loss)	15,672	8,422
Other comprehensive income (valuation allowance) [Abstract]
Change in unrealized investment gains and losses, net	(15,248)	(9,162)
Other comprehensive income (loss)	(15,248)	(9,162)
Other comprehensive income (net of tax) [Abstract]
Change in unrealized investment gains and losses, net (notes 7 and 8)	(45,918)	(25,604)
Unrealized foreign currency translation adjustment	1,083	917
Other comprehensive income (loss)	(44,835)	(24,687)
Accumulated other comprehensive income (loss) [Abstract]
Unrealized gains (losses) on investments	7,643		53,561
Defined benefit plans	(43,642)		(43,642)
Foreign currency translation adjustment	21,288		20,205
Total accumulated other comprehensive (loss) income	$ (14,711)		$ 30,124