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, 2018 USD ($)	Dec. 31, 2017 USD ($)
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	$ 222,034	$ 249,475
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	4,770	2,931
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	193,062	135,465
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	9,786	4,406
Debt Securities, Available-for-sale, Unrealized Loss Position	415,096	384,940
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss	$ 14,556	$ 7,337
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Number of Positions	110	60
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Number of Positions	81	76
Debt Securities, Available-for-sale, Unrealized Loss Position, Number of Positions	191	136
Corporate Debt Securities
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	$ 98,849	$ 85,642
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	2,692	1,250
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	76,271	44,640
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	3,996	1,597
Debt Securities, Available-for-sale, Unrealized Loss Position	175,120	130,282
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss	6,688	2,847
Collateralized Mortgage Backed Securities
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	0	1,381
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	0	45
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	6,089	5,237
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	337	135
Debt Securities, Available-for-sale, Unrealized Loss Position	6,089	6,618
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss	337	180
US Treasury Securities
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	43,284	75,811
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	314	198
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	12,168	9,302
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	392	198
Debt Securities, Available-for-sale, Unrealized Loss Position	55,452	85,113
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss	706	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	9,426	9,669
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	238	205
Debt Securities, Available-for-sale, Unrealized Loss Position	9,426	9,669
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss	238	205
US States and Political Subdivisions Debt Securities
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	72,880	83,682
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	1,651	1,348
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	86,243	66,617
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	4,722	2,271
Debt Securities, Available-for-sale, Unrealized Loss Position	159,123	150,299
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss	6,373	3,619
Debt Security, Government, Non-US
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	1,162	2,959
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	2	90
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	2,865	0
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	101	0
Debt Securities, Available-for-sale, Unrealized Loss Position	4,027	2,959
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss	103	$ 90
Redeemable Preferred Stock
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	5,859
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	111
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	5,859
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss	$ 111