5. Investment Securities: Schedule of Continuous Unrealized Loss Positions on Held-To-Maturity Investments (Details) Pure in Thousands	Jun. 30, 2018 USD ($)	Dec. 31, 2017 USD ($)
US Government Agencies Debt Securiities
Number of Securities	7	7
Less than Twelve Months, Fair Value	$ 240,000	$ 245,000
Less than 12 Months, Unrealized Losses	(10,000)	(5,000)
Twelve Months or Longer, Fair Value	2,004,000	2,028,000
12 Months or Longer, Unrealized Losses	(95,000)	(71,000)
Total Fair Value	2,244,000	2,273,000
Total Unrealized Losses	$ (105,000)	$ (76,000)
Mortgage-backed Securities, Issued by US Government Sponsored Enterprises
Number of Securities	14	8
Less than Twelve Months, Fair Value	$ 1,790,000	$ 1,124,000
Less than 12 Months, Unrealized Losses	(47,000)	(7,000)
Twelve Months or Longer, Fair Value	347,000	377,000
12 Months or Longer, Unrealized Losses	(20,000)	(11,000)
Total Fair Value	2,137,000	1,501,000
Total Unrealized Losses	$ (67,000)	$ (18,000)
Number of Securities	21	15
Less than Twelve Months, Fair Value	$ 2,030.000	$ 1,369,000
Less than 12 Months, Unrealized Losses	(57,000)	(12,000)
Twelve Months or Longer, Fair Value	2,351,000	2,405,000
12 Months or Longer, Unrealized Losses	(115,000)	(82,000)
Total Fair Value	4,381,000	3,774,000
Total Unrealized Losses	$ (172,000)	$ (94,000)