Fair Value Measurements, Changes in Level 3 Assets Measured on a Recurring Basis (Details) (USD $)	12 Months Ended
	Dec. 31, 2012 Security	Dec. 31, 2011 Security
Auction Rate Securities [Member]
Changes in Level 3 Assets Measured at Fair Value on a Recurring Basis [Roll Forward]
Beginning balance	$ 62,311,000	$ 88,129,000
Purchases	0	0
Settlements	(16,553,000)	(21,200,000)
Realized loss included in other income (expense), net	(2,699,000)	(4,750,000)
Reversal of pretax impairment charges included in accumulated other comprehensive income (loss)	3,224,000	132,000
Ending balance	46,283,000	62,311,000
Minimum estimated recovery period for auction rate securities (in months)	12 months
Number of auction rate securities sold or redeemed for full par value	1	2
Number of auction rate securities (ARS) sold in a secondary market	2
Number of auction rate securities (ARS) settled	3	2
Pre-tax gain on securities redeemed		100,000
Auction Rate Securities Collateralized by Student Loan Portfolios Guaranteed by U.S. Government [Member]
Changes in Level 3 Assets Measured at Fair Value on a Recurring Basis [Roll Forward]
Ending balance	46,283,000	54,300,000
Auction Rate Securities Collateralized by Student Loan Portfolios Which are Privately Insured [Member]
Changes in Level 3 Assets Measured at Fair Value on a Recurring Basis [Roll Forward]
Ending balance	$ 0	$ 8,000,000