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Securities Held to Maturity - Amortized Cost, Gross Unrecognized Gains and Losses and Fair Values of Securities (Detail) - USD ($) $ in Thousands | Sep. 30, 2019 | Jun. 30, 2019
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Schedule Of Held To Maturity Securities [Line Items] |  |  |
Amortized Cost |  | $ 37,888 | $ 576,652
Gross Unrecognized Gains |  | 802 | 8,734
Gross Unrecognized Losses |  | 7 | 708
Securities held to maturity, estimated fair value |  | 38,683 | 584,678
Corporate Bond [Member] |  |  |
Schedule Of Held To Maturity Securities [Line Items] |  |  |
Amortized Cost |  |  | 63,086
Gross Unrecognized Gains |  |  | 914
Fair Value |  |  | 64,000
Mortgage-Backed Securities [Member] |  |  |
Schedule Of Held To Maturity Securities [Line Items] |  |  |
Amortized Cost |  |  | 409,480
Gross Unrecognized Gains |  |  | 6,033
Gross Unrecognized Losses |  |  | 692
Securities held to maturity, estimated fair value |  |  | 414,821
Debt Securities [Member] |  |  |
Schedule Of Held To Maturity Securities [Line Items] |  |  |
Amortized Cost |  | 37,888 | 167,172
Gross Unrecognized Gains |  | 802 | 2,701
Gross Unrecognized Losses |  | 7 | 16
Fair Value |  | 38,683 | 169,857
Debt Securities [Member] | Obligations of State and Political Subdivisions [Member] |  |  |
Schedule Of Held To Maturity Securities [Line Items] |  |  |
Amortized Cost |  | 37,888 | 104,086
Gross Unrecognized Gains |  | 802 | 1,787
Gross Unrecognized Losses |  | 7 | 16
Fair Value |  | $ 38,683 | 105,857
Collateralized Mortgage Obligations Excluding Pass Through Securities [Member] |  |  |
Schedule Of Held To Maturity Securities [Line Items] |  |  |
Amortized Cost | [1] |  | 46,370
Gross Unrecognized Gains | [1] |  | 568
Gross Unrecognized Losses | [1] |  | 168
Securities held to maturity, estimated fair value | [1] |  | 46,770
Non-agency securities [Member] |  |  |
Schedule Of Held To Maturity Securities [Line Items] |  |  |
Amortized Cost |  |  | 11
Securities held to maturity, estimated fair value |  |  | 11
Residential Pass-Through Securities [Member] |  |  |
Schedule Of Held To Maturity Securities [Line Items] |  |  |
Amortized Cost | [1] |  | 166,283
Gross Unrecognized Gains | [1] |  | 1,961
Gross Unrecognized Losses | [1] |  | 518
Securities held to maturity, estimated fair value | [1] |  | 167,726
Commercial Pass-Through Securities [Member] |  |  |
Schedule Of Held To Maturity Securities [Line Items] |  |  |
Amortized Cost | [1] |  | 196,816
Gross Unrecognized Gains | [1] |  | 3,504
Gross Unrecognized Losses | [1] |  | 6
Securities held to maturity, estimated fair value | [1] |  | $ 200,314
[1] | Government-sponsored enterprises.

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