CONSOLIDATED STATEMENTS OF CHANGES IN STOCKHOLDERS' EQUITY (Unaudited) - USD ($) $ in Thousands	Total	Common Stock [Member]	Paid-in Capital [Member]	Retained Earnings [Member]	Unearned ESOP Shares [Member]	Accumulated Other Comprehensive (Loss) Income [Member]
Balance (in value) at Jun. 30, 2017	$ 1,057,181	$ 844	$ 728,790	$ 361,039	$ (34,536)	$ 1,044
Balance (in shares) at Jun. 30, 2017		84,351,000
Net Income	6,501			6,501
Other comprehensive income (loss), net of income tax expense (benefit)	5,368					5,368
ESOP shares committed to be released	1,476		503		973
Stock option exercise (in value)	102		102
Stock option exercise (in shares)		10,000
Stock option expense	1,045		1,045
Share repurchases (in value)	(69,314)	$ (48)	(69,266)
Stock repurchases (in shares)		(4,747,000)
Restricted stock plan shares earned	2,196		2,196
Cancellation of shares issued for restricted stock awards (in value)	(1,278)	$ (1)	(1,277)
Cancellation of shares issued for restricted stock awards (in shares)		(87,000)
Cash dividends declared	(14,004)			(14,004)
Balance (in value) at Dec. 31, 2017	989,273	$ 795	662,093	353,536	(33,563)	6,412
Balance (in shares) at Dec. 31, 2017		79,527,000
Balance (in value) at Sep. 30, 2017	1,014,233	$ 815	690,204	354,123	(34,049)	3,140
Balance (in shares) at Sep. 30, 2017		81,548,000
Net Income	1,269			1,269
Other comprehensive income (loss), net of income tax expense (benefit)	3,272					3,272
ESOP shares committed to be released	744		258		486
Stock option exercise (in value)	102		102
Stock option exercise (in shares)		10,000
Stock option expense	523		523
Share repurchases (in value)	(28,832)	$ (19)	(28,813)
Stock repurchases (in shares)		(1,944,000)
Restricted stock plan shares earned	1,096		1,096
Cancellation of shares issued for restricted stock awards (in value)	(1,278)	$ (1)	(1,277)
Cancellation of shares issued for restricted stock awards (in shares)		(87,000)
Cash dividends declared	(1,856)			(1,856)
Balance (in value) at Dec. 31, 2017	989,273	$ 795	662,093	353,536	(33,563)	6,412
Balance (in shares) at Dec. 31, 2017		79,527,000
Balance (in value) at Jun. 30, 2018	$ 1,268,748	$ 996	922,711	359,096	(32,590)	18,535
Balance (in shares) at Jun. 30, 2018	99,626,400	99,626,000
Cumulative effect of change in accounting principle for the adoption of ASU 2017-08 (Accounting Standards Update 2017-08 [Member]) at Jun. 30, 2018	$ (531)			(531)
Balance (in value), adjusted for change in accounting principle at Jun. 30, 2018	1,268,217	$ 996	922,711	358,565	(32,590)	18,535
Net Income	21,914			21,914
Other comprehensive income (loss), net of income tax expense (benefit)	(9,733)					(9,733)
ESOP shares committed to be released	1,339		366		973
Stock option expense	995		995
Share repurchases (in value)	(77,109)	$ (57)	(77,052)
Stock repurchases (in shares)		(5,785,000)
Issuance of shares under stock benefit plans (in value)		$ 1	(1)
Issuance of shares under stock benefit plans (in shares)		85,000
Restricted stock plan shares earned	2,068		2,068
Cancellation of shares issued for restricted stock awards (in value)	(944)	$ (2)	(942)
Cancellation of shares issued for restricted stock awards (in shares)		(154,000)
Cash dividends declared	(23,486)			(23,486)
Balance (in value) at Dec. 31, 2018	$ 1,183,261	$ 938	848,145	356,993	(31,617)	8,802
Balance (in shares) at Dec. 31, 2018	93,772,115	93,772,000
Balance (in value) at Sep. 30, 2018	$ 1,236,081	$ 978	897,551	350,838	(32,104)	18,818
Balance (in shares) at Sep. 30, 2018		97,754,000
Cumulative effect of change in accounting principle for the adoption of ASU 2017-08 (Accounting Standards Update 2017-08 [Member]) at Sep. 30, 2018	(531)			(531)
Balance (in value), adjusted for change in accounting principle at Sep. 30, 2018	1,235,550	$ 978	897,551	350,307	(32,104)	18,818
Net Income	10,768			10,768
Other comprehensive income (loss), net of income tax expense (benefit)	(10,016)					(10,016)
ESOP shares committed to be released	651		164		487
Stock option expense	495		495
Share repurchases (in value)	(50,193)	$ (38)	(50,155)
Stock repurchases (in shares)		(3,828,000)
Restricted stock plan shares earned	1,032		1,032
Cancellation of shares issued for restricted stock awards (in value)	(944)	$ (2)	(942)
Cancellation of shares issued for restricted stock awards (in shares)		(154,000)
Cash dividends declared	(4,082)			(4,082)
Balance (in value) at Dec. 31, 2018	$ 1,183,261	$ 938	$ 848,145	$ 356,993	$ (31,617)	$ 8,802
Balance (in shares) at Dec. 31, 2018	93,772,115	93,772,000