Accumulated Other Comprehensive Income- Schedule of Balances of Each Component (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Mar. 31, 2021	Mar. 31, 2020
Accumulated Other Comprehensive Income
Balance at the beginning of the period	$ 244,012	$ 232,589	$ 244,796	$ 216,490
Other comprehensive income (loss) before reclassifications	126	91	322	406
Reclassification to (earnings) loss	(83)	(61)	(247)	(193)
Net current-period other comprehensive income (loss)	43	30	75	213
Balance at the end of the period	236,459	238,250	236,459	238,250
Unrealized Investment Gain (Loss)
Accumulated Other Comprehensive Income
Balance at the beginning of the period	4	8	32	23
Other comprehensive income (loss) before reclassifications	(3)	2	(31)	(13)
Reclassification to (earnings) loss	0	0	0	0
Net current-period other comprehensive income (loss)	(3)	2	(31)	(13)
Balance at the end of the period	1	10	1	10
Postemployment Benefits Net Actuarial Gain (Loss)
Accumulated Other Comprehensive Income
Balance at the beginning of the period	2,165	2,112	2,105	1,914
Other comprehensive income (loss) before reclassifications	129	89	353	419
Reclassification to (earnings) loss	(83)	(61)	(247)	(193)
Net current-period other comprehensive income (loss)	46	28	106	226
Balance at the end of the period	2,211	2,140	2,211	2,140
Accumulated Other Comprehensive Income (Loss)
Accumulated Other Comprehensive Income
Balance at the beginning of the period	2,169	2,120	2,137	1,937
Balance at the end of the period	$ 2,212	$ 2,150	$ 2,212	$ 2,150