Significant Accounting Policies (Accumulated Other Comprehensive Income) (Details) (USD $)	3 Months Ended		6 Months Ended
	Jun. 30, 2013	Jun. 30, 2012	Jun. 30, 2013	Jun. 30, 2012
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	$ 10,300,000	$ 11,200,000	$ 26,984,000	$ 16,600,000
Other comprehensive income before reclassifications	(42,600,000)	3,900,000	(48,500,000)	6,300,000
Amounts reclassified from accumulated other comprehensive income	(3,300,000)	(7,400,000)	(14,100,000)	(15,200,000)
Other comprehensive loss, net of tax	(45,885,000)	(3,544,000)	(62,593,000)	(8,956,000)
Ending balance	(35,609,000)	7,700,000	(35,609,000)	7,700,000
Unrealized Gains (Losses) on investments available-for-sale [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	20,900,000	23,800,000	38,000,000	29,800,000
Other comprehensive income before reclassifications	(42,600,000)	3,900,000	(48,500,000)	6,300,000
Amounts reclassified from accumulated other comprehensive income	(3,700,000)	(8,100,000)	(14,900,000)	(16,500,000)
Other comprehensive loss, net of tax	(46,300,000)	(4,200,000)	(63,400,000)	(10,200,000)
Ending balance	(25,400,000)	19,600,000	(25,400,000)	19,600,000
Defined Benefit Pension Plans [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	(10,600,000)	(12,600,000)	(11,000,000)	(13,200,000)
Other comprehensive income before reclassifications	0	0	0	0
Amounts reclassified from accumulated other comprehensive income	400,000	700,000	800,000	1,300,000
Other comprehensive loss, net of tax	400,000	700,000	800,000	1,300,000
Ending balance	$ (10,200,000)	$ (11,900,000)	$ (10,200,000)	$ (11,900,000)