Investments in Debt and Marketable Equity Securities (and Certain Trading Assets) Disclosure [Text Block]: Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value (Details) $ in Thousands	Mar. 31, 2017 USD ($)	Dec. 31, 2016 USD ($)
Available For Sale Securities Continuous Unrealized Loss Position Less Than Twelve Months Fair Value	$ 264,475	$ 331,210
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	6,400	9,284
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	58,647	48,785
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	2,635	2,980
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	323,122	379,995
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	$ 9,035	$ 12,264
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Less than One Year	109	156
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Greater than or Equal to One Year	25	23
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions	134	179
Corporate Debt Securities
Available For Sale Securities Continuous Unrealized Loss Position Less Than Twelve Months Fair Value	$ 110,148	$ 145,205
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	2,557	3,818
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	14,565	19,841
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	1,413	1,672
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	124,713	165,046
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	3,970	5,490
Residential Mortgage Backed Securities
Available For Sale Securities Continuous Unrealized Loss Position Less Than Twelve Months Fair Value	7,138	5,038
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	142	116
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	0	0
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	0	0
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	7,138	5,038
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	142	116
US Treasury Securities
Available For Sale Securities Continuous Unrealized Loss Position Less Than Twelve Months Fair Value	24,076	28,406
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	382	441
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	0	0
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	0	0
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	24,076	28,406
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	382	441
US Government-sponsored Enterprises Debt Securities
Available For Sale Securities Continuous Unrealized Loss Position Less Than Twelve Months Fair Value	0	3,640
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	0	166
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	9,980	6,220
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	233	256
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	9,980	9,860
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	233	422
US States and Political Subdivisions Debt Securities
Available For Sale Securities Continuous Unrealized Loss Position Less Than Twelve Months Fair Value	119,213	144,357
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	3,194	4,561
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	29,118	18,132
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	884	554
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	148,331	162,489
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	4,078	5,115
Foreign Government Debt
Available For Sale Securities Continuous Unrealized Loss Position Less Than Twelve Months Fair Value	3,067	3,738
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	107	157
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	0	0
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	0	0
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	3,067	3,738
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	107	157
Redeemable Preferred Stock
Available For Sale Securities Continuous Unrealized Loss Position Less Than Twelve Months Fair Value	0	0
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	0	0
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	3,683	3,315
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	80	448
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	3,683	3,315
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	80	448
Debt Securities
Available For Sale Securities Continuous Unrealized Loss Position Less Than Twelve Months Fair Value	263,642	330,384
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	6,382	9,259
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	57,346	47,508
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	2,610	2,930
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	320,988	377,892
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	8,992	12,189
Nonredeemable Preferred Stock
Available For Sale Securities Continuous Unrealized Loss Position Less Than Twelve Months Fair Value	833	826
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	18	25
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	1,301	1,277
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	25	50
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	2,134	2,103
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	43	75
Equity Securities
Available For Sale Securities Continuous Unrealized Loss Position Less Than Twelve Months Fair Value	833	826
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	18	25
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	1,301	1,277
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	25	50
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	2,134	2,103
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	$ 43	$ 75