Supplemental Information (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended		9 Months Ended
	Sep. 30, 2012	Sep. 30, 2011	Sep. 30, 2012	Sep. 30, 2011
Supplemental Information
Income taxes paid	$ 44,531	$ 31,366	$ 83,979	$ 88,973
Interest paid	1,321	785	13,321	12,937
Dividends declared but not paid at year end	16,728	16,535	16,728	16,535
Proceeds from Sale of Available-for-sale Securities, Debt	75,397	248,201	293,969	494,532
Proceeds from Sale of Available-for-sale Securities, Equity	$ 5,406		$ 7,145