Employee Benefit Plans: Employee Benefit Plans (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Defined Benefit Pension Plans
Defined Benefit Plan, Net Periodic Benefit Cost [Abstract]
Service cost	$ 1,494	$ 1,362	$ 2,988	$ 2,724
Interest cost	3,880	3,963	7,760	7,926
Expected return on plan assets	(4,867)	(4,516)	(9,734)	(9,032)
Prior service cost (benefit)	15	16	30	32
Net loss (gain)	2,759	1,201	5,518	2,403
Net periodic benefit cost	3,281	2,026	6,562	4,053
Pension and Other Postretirement Benefit Contributions [Abstract]
Contributions by Employer	0		0
Estimated Future Employer Contributions in Current Fiscal Year			10,200
Estimated Future Employer Contributions in Next Fiscal Year			10,200
Defined Benefit Postretirement Healthcare Plans
Defined Benefit Plan, Net Periodic Benefit Cost [Abstract]
Service cost	464	425	928	850
Interest cost	450	480	900	959
Expected return on plan assets	(33)	(21)	(66)	(42)
Prior service cost (benefit)	(107)	(107)	(214)	(214)
Net loss (gain)	102	40	204	80
Net periodic benefit cost	876	817	1,752	1,633
Pension and Other Postretirement Benefit Contributions [Abstract]
Contributions by Employer	939		1,878
Estimated Future Employer Contributions in Current Fiscal Year			1,877
Estimated Future Employer Contributions in Next Fiscal Year			4,026
Supplemental Non-qualified Defined Benefit and Defined Contribution Plans
Defined Benefit Plan, Net Periodic Benefit Cost [Abstract]
Service cost	392	374	883	749
Interest cost	364	362	728	724
Prior service cost (benefit)	1	1	2	1
Net loss (gain)	270	124	540	249
Net periodic benefit cost	1,027	$ 861	2,153	$ 1,723
Pension and Other Postretirement Benefit Contributions [Abstract]
Contributions by Employer	$ 372		744
Estimated Future Employer Contributions in Current Fiscal Year			743
Estimated Future Employer Contributions in Next Fiscal Year			$ 1,544