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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
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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Amount of investment in debt security measured at amortized cost (held-to-maturity).

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