Summary of Significant Accounting Policies (Accumulated Other Comprehensive Income) (Details) (USD $)	12 Months Ended
	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	$ (32,867,000)	$ 27,000,000	$ 16,600,000
Other comprehensive income (loss) before reclassifications	31,000,000	(45,900,000)	31,700,000
Amounts reclassified from accumulated other comprehensive income	(1,400,000)	(14,000,000)	(21,300,000)
Other comprehensive income (loss), net of tax	29,606,000	(59,851,000)	10,352,000
Ending balance	(3,261,000)	(32,867,000)	27,000,000
Unrealized Gains (Losses) on investments available-for-sale [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	(28,300,000)	38,000,000	29,800,000
Other comprehensive income (loss) before reclassifications	38,300,000	(50,700,000)	32,100,000
Amounts reclassified from accumulated other comprehensive income	(1,800,000)	(15,600,000)	(23,900,000)
Other comprehensive income (loss), net of tax	36,500,000	(66,300,000)	8,200,000
Ending balance	8,200,000	(28,300,000)	38,000,000
Defined Benefit Pension Plans [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	(4,600,000)	(11,000,000)	(13,200,000)
Other comprehensive income (loss) before reclassifications	(7,300,000)	4,800,000	(400,000)
Amounts reclassified from accumulated other comprehensive income	400,000	1,600,000	2,600,000
Other comprehensive income (loss), net of tax	(6,900,000)	6,400,000	2,200,000
Ending balance	$ (11,500,000)	$ (4,600,000)	$ (11,000,000)