Other Comprehensive Income (Loss) - Summary of Accumulated Other Comprehensive Income (Loss) (Detail) - USD ($) $ in Thousands	3 Months Ended						9 Months Ended
	Mar. 31, 2020	Dec. 31, 2019	Sep. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Mar. 31, 2020	Mar. 31, 2019
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	$ 279,839	$ 281,522	$ 281,307	$ 288,782	$ 289,877	$ 287,559	$ 281,307	$ 287,559
Total other comprehensive income	244	360	256	720	478	1	860	1,199
Ending Balance	272,417	279,839	281,522	278,316	288,782	289,877	272,417	278,316
Net Unrealized Gain (Loss) on Available for Sale Securities [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	(34)		(209)	(1,300)		(1,536)	(209)	(1,536)
Other comprehensive income before reclassifications	186			757			406	1,110
Amounts reclassified from accumulated other comprehensive income	(20)						(20)	(55)
Less tax effect	(35)			(160)			(80)	(222)
Total other comprehensive income	131			597			306	833
Ending Balance	97	(34)		(703)	(1,300)		97	(703)
Unrealized Losses on Retirement Plans [Member] | Pension Benefits [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	(4,207)		(4,631)	(4,921)		(5,150)	(4,631)	(5,150)
Amounts reclassified from accumulated other comprehensive income	132			145			668	435
Less tax effect	(27)			(30)			(139)	(91)
Total other comprehensive income	105			115			529	344
Ending Balance	(4,102)	(4,207)		(4,806)	(4,921)		(4,102)	(4,806)
Unrealized Losses on Retirement Plans [Member] | SERP Benefits [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	(233)		(250)	(250)		(264)	(250)	(264)
Amounts reclassified from accumulated other comprehensive income	11			9			34	27
Less tax effect	(3)			(1)			(9)	(5)
Total other comprehensive income	8			8			25	22
Ending Balance	(225)	(233)		(242)	(250)		(225)	(242)
Accumulated Other Comprehensive Income (Loss) [Member]
Accumulated Other Comprehensive Income (Loss) [Line Items]
Beginning Balance	(4,474)	(4,834)	(5,090)	(6,471)	(6,949)	(6,950)	(5,090)	(6,950)
Other comprehensive income before reclassifications	186			757			406	1,110
Amounts reclassified from accumulated other comprehensive income	123			154			682	407
Less tax effect	(65)			(191)			(228)	(318)
Total other comprehensive income	244	360	256	720	478	1	860	1,199
Ending Balance	$ (4,230)	$ (4,474)	$ (4,834)	$ (5,751)	$ (6,471)	$ (6,949)	$ (4,230)	$ (5,751)