Significant Accounting Policies (Reclassifications Out of Accumulated Other Comprehensive Income) (Details) - USD ($) $ in Thousands		3 Months Ended		9 Months Ended
		Sep. 30, 2015	Sep. 30, 2014	Sep. 30, 2015	Sep. 30, 2014
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Income from operations before income taxes		$ 153,348	$ 22,723	$ 353,159	$ 183,485
Tax expense (benefit)		93,095	31,662	204,550	42,770
Reclassification out of Accumulated Other Comprehensive Income [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Net of tax		(500)	100	100	1,400
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		(100)	300	2,100	2,600
Income from operations before income taxes		(100)	300	2,100	2,600
Tax expense (benefit)		0	100	800	900
Net of tax		(100)	200	1,300	1,700
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	[1]	(100)	(100)	(300)	(300)
Actuarial gains (losses)	[1]	(500)	(100)	(1,600)	(200)
Income from operations before income taxes		(600)	(200)	(1,900)	(500)
Tax expense (benefit)		(200)	(100)	(700)	(200)
Net of tax		$ (400)	$ (100)	$ (1,200)	$ (300)

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