Significant Accounting Policies (Reclassification of AOCI) (Details) (USD $)	12 Months Ended
	Dec. 31, 2013		Dec. 31, 2012		Dec. 31, 2011
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Income tax provision	$ 99,827,000		$ 5,969,000		$ 100,708,000
Reclassification out of Accumulated Other Comprehensive Income [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Total reclassifications for the period	14,000,000		21,300,000		21,200,000
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]
Unrealized gains on investments available-for-sale	24,000,000		36,700,000		33,000,000
Total before tax	24,000,000		36,700,000		33,000,000
Income tax provision	8,400,000		12,800,000		11,500,000
Total reclassifications for the period	15,600,000		23,900,000		21,500,000
Reclassification out of Accumulated Other Comprehensive Income [Member] | Defined Benefit Pension Plans [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Prior-service cost	(100,000)	[1]	(100,000)	[1]	0	[1]
Actuarial gains (losses)	(2,500,000)	[1]	(4,100,000)	[1]	(600,000)	[1]
Total before tax	(2,600,000)		(4,200,000)		(600,000)
Income tax provision	(1,000,000)		(1,600,000)		(300,000)
Total reclassifications for the period	$ (1,600,000)		$ (2,600,000)		$ (300,000)

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