Significant Accounting Policies (Comprehensive Income) (Details) (USD $)	12 Months Ended
	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010
Accounting Policies [Abstract]
Beginning balance, Unrealized gains (losses) on investments available-for-sale	$ 29,800,000	$ 5,300,000	$ 1,000,000
Other comprehensive income (loss) for the year, Unrealized gains (losses) on investments available-for-sale	8,200,000	24,500,000	4,300,000
Ending balance, Unrealized gains (losses) on investments available-for-sale	38,000,000	29,800,000	5,300,000
Beginning balance, Defined Benefit Pension Plans	(13,200,000)	(4,800,000)	(900,000)
Other compehrensive income (loss) for the year, Defined Benefit Pension Plans	2,200,000	(8,400,000)	(3,900,000)
Ending balance, Defined Benefit Pension Plans	(11,000,000)	(13,200,000)	(4,800,000)
Beginning balance, Accumulated Other Comprehensive Income (Loss)	16,632,000	500,000	100,000
Other comprehensive income, net of tax	10,352,000	16,145,000	435,000
Ending balance, Accumulated Other Comprehensive Income (Loss)	$ 26,984,000	$ 16,632,000	$ 500,000