Income Taxes - Federal Statutory Rate Reconciliation (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
Income Tax Disclosure [Abstract]
Income before income taxes	$ 68,847	$ 69,895	$ 32,081
Income Tax Statutory Rate Reconciliation [Abstract]
Income tax at federal statutory rate	14,458	14,678	6,737
Increase (decrease) in taxes attributable to:
State taxes, net of federal income tax benefit	4,572	4,142	2,251
Uncertain tax positions	1,678	1,351	323
Property flow-through	(8,573)	(9,215)	(2,054)
Capitalized merger costs	0	(296)	5,350
Tax reform - rate change impact on deferred taxes	0	0	77
Reversal of excess deferred taxes recognized in regulatory liability	(3,295)	(2,912)	(2,355)
Pension flow-through	429	92	(1,244)
Stock-based compensation	(331)	(333)	(223)
Other items, net	(569)	873	(408)
Income tax expense (benefit)	$ 8,369	$ 8,380	$ 8,454