Summary of Significant Accounting Policies (Reclassification of AOCI) (Details) (USD $)	12 Months Ended
	Dec. 31, 2014		Dec. 31, 2013		Dec. 31, 2012
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Income tax provision	$ 54,163,000		$ 99,827,000		$ 5,969,000
Reclassification out of Accumulated Other Comprehensive Income [Member]
Reclassification Adjustment out of Accumulated Other Comprehensive Income [Line Items]
Net of tax	1,400,000		14,000,000		21,300,000
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	2,700,000		24,000,000		36,700,000
Income from operations before income taxes	2,700,000		24,000,000		36,700,000
Income tax provision	900,000		8,400,000		12,800,000
Net of tax	1,800,000		15,600,000		23,900,000
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	(400,000)	[1]	(100,000)	[1]	(100,000)	[1]
Actuarial gains (losses)	(200,000)	[1]	(2,500,000)	[1]	(4,100,000)	[1]
Income from operations before income taxes	(600,000)		(2,600,000)		(4,200,000)
Income tax provision	(200,000)		(1,000,000)		(1,600,000)
Net of tax	$ (400,000)		$ (1,600,000)		$ (2,600,000)

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