Impairment of Securities - Schedule of Temporary Impairment Losses, Investments (Detail) - USD ($) $ in Thousands	Dec. 31, 2018	Jun. 30, 2018
Schedule Of Held To Maturity Securities [Line Items]
Less than 12 Months: Fair Value	$ 150,857	$ 476,641
Less than 12 Months: Unrecognized Losses	1,047	7,824
12 Months or More: Fair Value	348,562	78,832
12 Months or More: Unrecognized Losses	5,511	2,548
Total: Fair Value	499,419	555,473
Total: Unrecognized Losses	6,558	10,372
Debt Securities [Member]
Schedule Of Held To Maturity Securities [Line Items]
Total: Unrecognized Losses	1,960	2,149
Debt Securities [Member] | Obligations of State and Political Subdivisions [Member]
Schedule Of Held To Maturity Securities [Line Items]
Less than 12 Months: Fair Value	8,438	86,678
Less than 12 Months: Unrecognized Losses	28	1,662
12 Months or More: Fair Value	74,429	3,151
12 Months or More: Unrecognized Losses	1,321	203
Total: Fair Value	82,867	89,829
Total: Unrecognized Losses	1,349	1,865
Debt Securities [Member] | Subordinated Debt [Member]
Schedule Of Held To Maturity Securities [Line Items]
Less than 12 Months: Fair Value	42,319	41,010
Less than 12 Months: Unrecognized Losses	410	284
12 Months or More: Fair Value	4,798
12 Months or More: Unrecognized Losses	201
Total: Fair Value	47,117	41,010
Total: Unrecognized Losses	611	284
Collateralized Mortgage Obligations Excluding Pass Through Securities [Member]
Schedule Of Held To Maturity Securities [Line Items]
Less than 12 Months: Fair Value		42,712
Less than 12 Months: Unrecognized Losses		753
12 Months or More: Fair Value	28,532	12,730
12 Months or More: Unrecognized Losses	771	595
Total: Fair Value	28,532	55,442
Total: Unrecognized Losses	771	1,348
Residential Pass-Through Securities [Member]
Schedule Of Held To Maturity Securities [Line Items]
Less than 12 Months: Fair Value	48,722	133,859
Less than 12 Months: Unrecognized Losses	193	2,258
12 Months or More: Fair Value	125,969	61,760
12 Months or More: Unrecognized Losses	2,496	1,747
Total: Fair Value	174,691	195,619
Total: Unrecognized Losses	2,689	4,005
Commercial Pass-Through Securities [Member]
Schedule Of Held To Maturity Securities [Line Items]
Less than 12 Months: Fair Value	51,378	172,382
Less than 12 Months: Unrecognized Losses	416	2,867
12 Months or More: Fair Value	114,834	1,191
12 Months or More: Unrecognized Losses	722	3
Total: Fair Value	166,212	173,573
Total: Unrecognized Losses	$ 1,138	$ 2,870