Significant Accounting Policies (Reclassifications Out of Accumulated Other Comprehensive Income) (Details) (USD $)	3 Months Ended				9 Months Ended
	Sep. 30, 2013		Sep. 30, 2012		Sep. 30, 2013		Sep. 30, 2012
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Tax benefit	$ 41,740,000		$ 8,898,000		$ 91,538,000		$ 5,712,000
Reclassification out of Accumulated Other Comprehensive Income [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Net of tax	(200,000)		2,200,000		13,900,000		17,400,000
Reclassification out of Accumulated Other Comprehensive Income [Member] | Unrealized gains (losses) on investments available-for-sale [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Net investment income	300,000		4,300,000		23,300,000		29,700,000
Total before tax	300,000		4,300,000		23,300,000		29,700,000
Tax benefit	100,000		1,500,000		8,200,000		10,400,000
Net of tax	200,000		2,800,000		15,100,000		19,300,000
Reclassification out of Accumulated Other Comprehensive Income [Member] | Amortization of defined benefit pension items [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Prior-service cost	(100,000)	[1]	0	[1]	(100,000)	[1]	(100,000)	[1]
Actuarial gains (losses)	(600,000)	[1]	(1,000,000)	[1]	(1,900,000)	[1]	(3,000,000)	[1]
Total before tax	(700,000)		(1,000,000)		(2,000,000)		(3,100,000)
Tax benefit	(300,000)		(400,000)		(800,000)		(1,200,000)
Net of tax	$ (400,000)		$ (600,000)		$ (1,200,000)		$ (1,900,000)

[1] These accumulated other comprehensive income components are included in the computation of net periodic pension cost.