Employee Benefit Plans Employee Benefit Plans 14 (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Amounts recognized on the balance sheets:
Non-current liabilities				$ 68,469	$ 57,636
SERP
Amounts recognized on the balance sheets:
Current liabilities				(609)	(433)
Non-current liabilities				29,094	24,084
Net amount recognized				(29,703)	(24,517)
Amounts recognized in regulatory assets consist of:
Prior service cost (credit)				0	0
Net loss				8,352	5,403
Regulatory assets (liabilities)	$ 5,403	$ 5,403	$ 7,556	8,352	5,403	$ 7,556
Unfunded accrued pension cost				21,351	19,114
Net liability (asset) recognized				29,703	24,517
Changes in plan assets and benefit obligations recognized in regulatory assets:
Regulatory asset at beginning of year	5,403	7,556
Net (gain) loss	3,419	(1,104)
Amortization of prior service (cost) credit	0	0
Amortization of net gain (loss)	(470)	(1,049)
Change in regulatory asset	2,949	(2,153)
Regulatory asset (liability) at end of year	8,352	5,403	7,556
Net periodic pension costs	2,733	3,033	$ 2,612
Change in regulatory asset	2,949	(2,153)
Total recognized in net periodic pension cost and regulatory asset (liability)	5,682	880
Estimated amounts that will be amortized from regulatory asset over the next fiscal year:
Initial net asset (obligation)	0	0
Prior service cost	0	0
Net gain (loss)	$ (844)	$ (471)
Additional year-end information for plans with an accumulated benefit obligation in excess of plan assets:
Projected benefit obligation				29,703	24,517	$ 24,062
Accumulated benefit obligation				26,251	21,229
Fair value of plan assets				$ 0	$ 0
Weighted-average assumptions used to determine benefit obligations at December 31:
Discount rate				3.36%	4.40%
Rate of compensation increase				4.00%	4.00%