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	Jun. 30, 2017 USD ($)	Dec. 31, 2016 USD ($)
Available For Sale Securities Continuous Unrealized Loss Position Less Than Twelve Months Fair Value	$ 240,809	$ 331,210
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	3,612	9,284
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	62,742	48,785
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	2,877	2,980
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	303,551	379,995
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	$ 6,489	$ 12,264
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Less than One Year	108	156
Available-for-sale, Securities in Unrealized Loss Positions, Qualitative Disclosure, Number of Positions, Greater than or Equal to One Year	26	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	$ 107,013	$ 145,205
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	1,511	3,818
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	17,151	19,841
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	1,304	1,672
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	124,164	165,046
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	2,815	5,490
Residential Mortgage Backed Securities
Available For Sale Securities Continuous Unrealized Loss Position Less Than Twelve Months Fair Value	5,522	5,038
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	107	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	5,522	5,038
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	107	116
US Treasury Securities
Available For Sale Securities Continuous Unrealized Loss Position Less Than Twelve Months Fair Value	29,830	28,406
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	250	441
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	781	0
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	19	0
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	30,611	28,406
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	269	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	9,878	6,220
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	202	256
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	9,878	9,860
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	202	422
US States and Political Subdivisions Debt Securities
Available For Sale Securities Continuous Unrealized Loss Position Less Than Twelve Months Fair Value	98,444	144,357
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	1,744	4,561
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	28,241	18,132
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	1,148	554
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	126,685	162,489
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	2,892	5,115
Foreign Government Debt
Available For Sale Securities Continuous Unrealized Loss Position Less Than Twelve Months Fair Value	0	3,738
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	0	157
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	3,042	0
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	90	0
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	3,042	3,738
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	90	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	3,649	3,315
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	114	448
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	3,649	3,315
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	114	448
Debt Securities
Available For Sale Securities Continuous Unrealized Loss Position Less Than Twelve Months Fair Value	240,809	330,384
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	3,612	9,259
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value	62,742	47,508
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	2,877	2,930
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value	303,551	377,892
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss	$ 6,489	12,189
Nonredeemable Preferred Stock
Available For Sale Securities Continuous Unrealized Loss Position Less Than Twelve Months Fair Value		826
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss		25
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value		1,277
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss		50
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value		2,103
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss		75
Equity Securities
Available For Sale Securities Continuous Unrealized Loss Position Less Than Twelve Months Fair Value		826
Available-for-sale Securities, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss		25
Available-for-sale Securities, Continuous Unrealized Loss Position, Twelve Months or Longer, Fair Value		1,277
Available-for-sale Securities, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss		50
Available-for-sale Securities, Continuous Unrealized Loss Position, Fair Value		2,103
Available-for-sale Securities, Continuous Unrealized Loss Position, Accumulated Loss		$ 75