Investments in Debt and Equity Securities (Details) (USD $) In Thousands, unless otherwise specified	Sep. 30, 2012	Dec. 31, 2011
Amortized costs and fair values
Equity securities, Amortized costs	$ 9,348	$ 5,005
Total, Amortized costs	459,641	449,552
Debt securities, Fair values	472,923
Equity securities, Fair values	10,857	5,443
Available for sale securities, Total	483,780	460,985
Municipal [Member]
Amortized costs and fair values
Debt securities, Amortized costs	16,903	26,721
Debt securities, Fair values	17,892	27,801
Corporate and utilities [Member]
Amortized costs and fair values
Debt securities, Amortized costs	246,332	237,912
Debt securities, Fair values	265,255	244,123
Foreign [Member]
Amortized costs and fair values
Debt securities, Amortized costs	169,834	162,384
Debt securities, Fair values	171,026	164,268
U.S. Government [Member]
Amortized costs and fair values
Debt securities, Amortized costs	17,224	17,530
Debt securities, Fair values	$ 18,750	$ 19,350