Debt And Equity Securities (Amortized Cost And Estimated Fair Value Of Debt Securities) (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2012	Dec. 31, 2011
Schedule of Trading Securities and Other Trading Assets [Line Items]
Amortized cost	$ 37,553	$ 42,100
Estimated fair value	2,186,123	2,201,911
U.S. Treasury Bonds [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Amortized cost, Due in one year or less	45,702
Estimated fair value, Due in one year or less	45,973
Amortized cost, Due after one through five years	19,278
Estimated fair value, Due after one through five years	20,682
Amortized cost, Due after five through ten years	43,921
Estimated fair value, Due after five through ten years	43,219
Amortized cost, Due after ten years	134
Estimated fair value, Due after ten years	188
Amortized cost	109,035
Estimated fair value	110,062
Municipal Bonds [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Amortized cost, Due in one year or less	2,131
Estimated fair value, Due in one year or less	2,158
Amortized cost, Due after one through five years	102,850
Estimated fair value, Due after one through five years	106,599
Amortized cost, Due after five through ten years	139,977
Estimated fair value, Due after five through ten years	148,652
Amortized cost, Due after ten years	112,414
Estimated fair value, Due after ten years	117,302
Amortized cost	357,372
Estimated fair value	374,711
Foreign Bonds [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Amortized cost, Due in one year or less	33,455
Estimated fair value, Due in one year or less	33,785
Amortized cost, Due after one through five years	160,494
Estimated fair value, Due after one through five years	161,865
Amortized cost, Due after five through ten years	30,934
Estimated fair value, Due after five through ten years	30,765
Amortized cost	224,883
Estimated fair value	226,415
Governmental Agency Bonds [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Amortized cost, Due in one year or less	2,343
Estimated fair value, Due in one year or less	2,376
Amortized cost, Due after one through five years	83,363
Estimated fair value, Due after one through five years	83,726
Amortized cost, Due after five through ten years	69,862
Estimated fair value, Due after five through ten years	69,751
Amortized cost, Due after ten years	17,491
Estimated fair value, Due after ten years	17,933
Amortized cost	173,059
Estimated fair value	173,786
Corporate Debt Securities [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Amortized cost, Due in one year or less	5,137
Estimated fair value, Due in one year or less	5,190
Amortized cost, Due after one through five years	103,615
Estimated fair value, Due after one through five years	106,697
Amortized cost, Due after five through ten years	134,485
Estimated fair value, Due after five through ten years	140,737
Amortized cost, Due after ten years	19,484
Estimated fair value, Due after ten years	20,234
Amortized cost	262,721
Estimated fair value	272,858
Total Debt Securities Excluding Mortgage-Backed Securities [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Amortized cost, Due in one year or less	88,768
Estimated fair value, Due in one year or less	89,482
Amortized cost, Due after one through five years	469,600
Estimated fair value, Due after one through five years	479,569
Amortized cost, Due after five through ten years	419,179
Estimated fair value, Due after five through ten years	433,124
Amortized cost, Due after ten years	149,523
Estimated fair value, Due after ten years	155,657
Amortized cost	1,127,070
Estimated fair value	1,157,832
Total Mortgage-Backed Securities [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Amortized cost	1,026,843
Estimated fair value	1,028,291
Debt Securities [Member]
Schedule of Trading Securities and Other Trading Assets [Line Items]
Amortized cost	2,153,913
Estimated fair value	$ 2,186,123