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	Sep. 30, 2018 USD ($)	Dec. 31, 2017 USD ($)
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	$ 205,783	$ 249,475
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	5,272	2,931
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	213,196	135,465
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	10,553	4,406
Debt Securities, Available-for-sale, Unrealized Loss Position	418,979	384,940
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss	$ 15,825	$ 7,337
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Number of Positions	99	60
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Number of Positions	96	76
Debt Securities, Available-for-sale, Unrealized Loss Position, Number of Positions	195	136
Corporate Debt Securities
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	$ 98,623	$ 85,642
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	2,949	1,250
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	88,261	44,640
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	3,933	1,597
Debt Securities, Available-for-sale, Unrealized Loss Position	186,884	130,282
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss	6,882	2,847
Collateralized Mortgage Backed Securities
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	859	1,381
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	57	45
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	5,106	5,237
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	331	135
Debt Securities, Available-for-sale, Unrealized Loss Position	5,965	6,618
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss	388	180
US Treasury Securities
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	39,740	75,811
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	328	198
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	8,388	9,302
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	402	198
Debt Securities, Available-for-sale, Unrealized Loss Position	48,128	85,113
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss	730	396
US Government-sponsored Enterprises Debt Securities
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	0	0
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	0	0
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	9,318	9,669
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	347	205
Debt Securities, Available-for-sale, Unrealized Loss Position	9,318	9,669
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss	347	205
US States and Political Subdivisions Debt Securities
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	59,619	83,682
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	1,753	1,348
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	99,307	66,617
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	5,433	2,271
Debt Securities, Available-for-sale, Unrealized Loss Position	158,926	150,299
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss	7,186	3,619
Debt Security, Government, Non-US
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	1,145	2,959
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	12	90
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	2,816	0
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	107	0
Debt Securities, Available-for-sale, Unrealized Loss Position	3,961	2,959
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss	119	$ 90
Redeemable Preferred Stock
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	5,797
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	173
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	0
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	0
Debt Securities, Available-for-sale, Unrealized Loss Position	5,797
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss	$ 173