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, 2018 USD ($)	Dec. 31, 2017 USD ($)
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	$ 219,681	$ 249,475
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	3,864	2,931
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	188,699	135,465
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	8,150	4,406
Debt Securities, Available-for-sale, Unrealized Loss Position	408,380	384,940
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss	$ 12,014	$ 7,337
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Number of Positions	79	60
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Number of Positions	86	76
Debt Securities, Available-for-sale, Unrealized Loss Position, Number of Positions	165	136
Corporate Debt Securities
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	$ 71,323	$ 85,642
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	1,933	1,250
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	75,976	44,640
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	3,311	1,597
Debt Securities, Available-for-sale, Unrealized Loss Position	147,299	130,282
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss	5,244	2,847
Collateralized Mortgage Backed Securities
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	48	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	6,318	5,237
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	327	135
Debt Securities, Available-for-sale, Unrealized Loss Position	6,366	6,618
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss	327	180
US Treasury Securities
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	71,743	75,811
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	454	198
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	9,032	9,302
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	354	198
Debt Securities, Available-for-sale, Unrealized Loss Position	80,775	85,113
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss	808	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	9,583	9,669
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	219	205
Debt Securities, Available-for-sale, Unrealized Loss Position	9,583	9,669
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss	219	205
US States and Political Subdivisions Debt Securities
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	69,540	83,682
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	1,363	1,348
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	84,881	66,617
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	3,840	2,271
Debt Securities, Available-for-sale, Unrealized Loss Position	154,421	150,299
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss	5,203	3,619
Debt Security, Government, Non-US
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months	1,168	2,959
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, Less than 12 Months, Accumulated Loss	3	90
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer	2,909	0
Debt Securities, Available-for-sale, Continuous Unrealized Loss Position, 12 Months or Longer, Accumulated Loss	99	0
Debt Securities, Available-for-sale, Unrealized Loss Position	4,077	2,959
Debt Securities, Available-for-sale, Unrealized Loss Position, Accumulated Loss	102	$ 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