Significant Accounting Policies (Accumulated Other Comprehensive Income) (Details) (USD $)	3 Months Ended
	Mar. 31, 2013	Mar. 31, 2012
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	$ 26,984,000	$ 16,600,000
Other comprehensive income before reclassifications	(5,900,000)	2,400,000
Amounts reclassified from accumulated other comprehensive income	(10,800,000)	(7,800,000)
Other comprehensive (loss) income, net of tax	(16,708,000)	(5,412,000)
Ending balance	10,276,000	11,200,000
Unrealized Gains (Losses) on investments available-for-sale [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	38,000,000	29,800,000
Other comprehensive income before reclassifications	(5,900,000)	2,400,000
Amounts reclassified from accumulated other comprehensive income	(11,200,000)	(8,400,000)
Other comprehensive (loss) income, net of tax	(17,100,000)	(6,000,000)
Ending balance	20,900,000	23,800,000
Defined Benefit Pension Plans [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning balance	(11,000,000)	(13,200,000)
Other comprehensive income before reclassifications	0	0
Amounts reclassified from accumulated other comprehensive income	400,000	600,000
Other comprehensive (loss) income, net of tax	400,000	600,000
Ending balance	$ (10,600,000)	$ (12,600,000)