Significant Accounting Policies (Reclassifications Out of Accumulated Other Comprehensive Income) (Details) (USD $)	3 Months Ended
	Mar. 31, 2015		Mar. 31, 2014
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Income from operations before income taxes	$ 67,709,000		$ 61,960,000
Tax expense (benefit)	37,721,000		33,173,000
Reclassification out of Accumulated Other Comprehensive Income [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Net of tax	0		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	600,000		300,000
Income from operations before income taxes	600,000		300,000
Tax expense (benefit)	200,000		100,000
Net of tax	400,000		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]	(100,000)	[1]
Actuarial gains (losses)	(500,000)	[1]	(100,000)	[1]
Income from operations before income taxes	(600,000)		(200,000)
Tax expense (benefit)	(200,000)		(100,000)
Net of tax	$ (400,000)		$ (100,000)

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