Significant Accounting Policies (Reclassifications Out of Accumulated Other Comprehensive Income) (Details) (USD $)	3 Months Ended
	Mar. 31, 2014		Mar. 31, 2013
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Income from operations before income taxes	$ 61,960,000		$ 81,303,000
Tax expense (benefit)	33,173,000		31,253,000
Reclassification out of Accumulated Other Comprehensive Income [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Net of tax	100,000		10,800,000
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 (losses) on investments available-for-sale	300,000		17,300,000
Income from operations before income taxes	300,000		17,300,000
Tax expense (benefit)	100,000		6,100,000
Net of tax	200,000		11,200,000
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]
Actuarial gains (losses)	(100,000)	[1]	(600,000)	[1]
Income from operations before income taxes	(200,000)		(600,000)
Tax expense (benefit)	(100,000)		(200,000)
Net of tax	$ (100,000)		$ (400,000)

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