Comprehensive (Loss) Income - Schedule of Accumulated Other Comprehensive (Loss) Income (Detail) - USD ($) $ in Thousands	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019
Accumulated Other Comprehensive Income Loss [Line Items]
Total Stockholders' Equity	$ 1,092,341	$ 1,124,060	$ 1,084,177	$ 1,094,570	$ 1,110,789	$ 1,127,159
Net Unrealized Gain on Securities Available for Sale [Member]
Accumulated Other Comprehensive Income Loss [Line Items]
Net unrealized gain on securities available for sale	23,958		22,482
Tax effect	(7,031)		(6,541)
Total Stockholders' Equity	16,927		15,941
Fair Value Adjustments on Derivatives [Member]
Accumulated Other Comprehensive Income Loss [Line Items]
Net unrealized gain on securities available for sale	(13,551)		(19,418)
Tax effect	4,039		5,730
Total Stockholders' Equity	(9,512)		(13,688)
Benefit Plan Adjustments [Member]
Accumulated Other Comprehensive Income Loss [Line Items]
Net unrealized gain on securities available for sale	(1,370)		(1,412)
Tax effect	408		416
Total Stockholders' Equity	(962)		(996)
Accumulated Other Comprehensive Income (Loss) [Member]
Accumulated Other Comprehensive Income Loss [Line Items]
Total Stockholders' Equity	$ 6,453	$ 3,974	$ 1,257	$ 7,955	$ 8,690	$ 2,839