Fair Value Of Financial Instruments (Quantitative Information related To The Significant Unobservable Inputs Utilized In Company's Level 3 Recurring Fair Value Measurements) (Details) (USD $) In Thousands, unless otherwise specified	6 Months Ended
	Jun. 30, 2012	Dec. 31, 2011
Available-for-sale securities, Estimated fair value	$ 1,329,359	$ 1,214,141
Investments, Fair Value Disclosure	180,080	211,208
State And Municipal Securities [Member]
Available-for-sale securities, Estimated fair value	119,603	86,932
Discount rate range, high end
Discount rate, weighted average	5.30%
Workout period range, high end
Weighted average workout period
Auction Rate Equity Securities [Member]
Investments, Fair Value Disclosure	80,037	103,176
Discount rate range, high end
Discount rate, weighted average	5.40%
Workout period range, high end
Weighted average workout period
Auction Rate Municipal Securities [Member]
Investments, Fair Value Disclosure	11,503	11,729
Discount rate range, high end
Discount rate, weighted average	4.90%
Workout period range, high end
Weighted average workout period
Level 3 [Member]
Available-for-sale securities, Estimated fair value	112,730	78,896
Investments, Fair Value Disclosure	130,631	151,938
Level 3 [Member] | State And Municipal Securities [Member]
Available-for-sale securities, Estimated fair value	100,730	66,896
Level 3 [Member] | Auction Rate Equity Securities [Member]
Investments, Fair Value Disclosure	80,037	103,176
Level 3 [Member] | Auction Rate Municipal Securities [Member]
Investments, Fair Value Disclosure	11,503	11,729
Estimated Fair Value [Member] | State And Municipal Securities [Member]
Available-for-sale securities, Estimated fair value	100,730
Estimated Fair Value [Member] | Auction Rate Equity Securities [Member]
Available-for-sale securities, Estimated fair value	80,037
Estimated Fair Value [Member] | Auction Rate Municipal Securities [Member]
Available-for-sale securities, Estimated fair value	$ 11,503