Significant Accounting Policies (Reclassifications Out of Accumulated Other Comprehensive Income) (Details) (USD $)	3 Months Ended				6 Months Ended
	Jun. 30, 2013		Jun. 30, 2012		Jun. 30, 2013		Jun. 30, 2012
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Tax benefit	$ 18,545,000		$ 2,241,000		$ 49,798,000		$ (3,186,000)
Reclassification out of Accumulated Other Comprehensive Income [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Net of tax	3,300,000		7,400,000		14,100,000		15,200,000
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	5,700,000		12,400,000		23,000,000		25,400,000
Total before tax	5,700,000		12,400,000		23,000,000		25,400,000
Tax benefit	2,000,000		4,300,000		8,100,000		8,900,000
Net of tax	3,700,000		8,100,000		14,900,000		16,500,000
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	0	[1]	(100,000)	[1]	0	[1]	(100,000)	[1]
Actuarial gains (losses)	(700,000)	[1]	(1,000,000)	[1]	(1,300,000)	[1]	(2,000,000)
Total before tax	(700,000)		(1,100,000)		(1,300,000)		(2,100,000)
Tax benefit	(300,000)		(400,000)		(500,000)		(800,000)
Net of tax	$ (400,000)		$ (700,000)		$ (800,000)		$ (1,300,000)

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