Significant Accounting Policies (Reclassifications Out of Accumulated Other Comprehensive Income) (Details) (USD $)	3 Months Ended				6 Months Ended
	Jun. 30, 2014		Jun. 30, 2013		Jun. 30, 2014		Jun. 30, 2013
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Income from operations before income taxes	$ 98,802,000		$ 52,028,000		$ 160,762,000		$ 133,331,000
Tax expense (benefit)	(22,065,000)		18,545,000		11,108,000		49,798,000
Reclassification out of Accumulated Other Comprehensive Income [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Net of tax	1,200,000		3,300,000		1,300,000		14,100,000
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	1,900,000		5,700,000		2,200,000		23,000,000
Income from operations before income taxes	1,900,000		5,700,000		2,200,000		23,000,000
Tax expense (benefit)	600,000		2,000,000		700,000		8,100,000
Net of tax	1,300,000		3,700,000		1,500,000		14,900,000
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]	(200,000)	[1]	0	[1]
Actuarial gains (losses)	0	[1]	(700,000)	[1]	(100,000)	[1]	(1,300,000)	[1]
Income from operations before income taxes	(100,000)		(700,000)		(300,000)		(1,300,000)
Tax expense (benefit)	0		(300,000)		(100,000)		(500,000)
Net of tax	$ (100,000)		$ (400,000)		$ (200,000)		$ (800,000)

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