CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY (Unaudited) - USD ($) $ in Thousands	Total	Paid In Capital [Member]	Retained Earnings [Member]	Accumulated Other Comprehensive Income (Loss) [Member]	Treasury Stock [Member]	Maximum Cash Obligation Related To ESOP Shares [Member]
Beginning Balance at Dec. 31, 2018	$ 334,882	$ 52,122	$ 371,848	$ (3,250)	$ (36,968)	$ (48,870)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of 1,468, 13,120, 87,959 and 105,542 shares of common stock for 3 months ended September 30, 2019 and 2020 and the 9 months ended September 30, 2019 and 2020, respectively	5,374	3,072			2,302
Issuance 1,786, 1,861, 5,821, and 5,430 shares of common stock under the employee stock purchase plan for 3 months ended September 30, 2019 and 2020 and the 9 months ended September 30, 2019 and 2020, respectively	325	325
Unearned restricted stock compensation	572	572
Forfeiture of 134, 3,188, 5,255 and 4,211 shares of common stock for 3 months ended September 30, 2019 and 2020 and the 9 months ended September 30, 2019 and 2020, respectively	(262)	(262)
Share-based compensation	7	7
Change related to ESOP shares	(2,432)					(2,432)
Net income	33,705		33,705
Cash dividends ($0.82 and $0.89 per share for 9 months ended September 30, 2019 and 2020, respectively)	(7,657)		(7,657)
Purchase of 8,209, 29,807, 83,606 and 112,407 shares of common stock for 3 months ended September 30, 2019 and 2020 and the 9 months ended September 30, 2019 and 2020, respectively	(5,177)				(5,177)
Other comprehensive income	4,498			4,498
Ending Balance at Sep. 30, 2019	363,835	55,836	397,896	1,248	(39,843)	(51,302)
Beginning Balance at Jun. 30, 2019	353,524	55,515	386,614	972	(39,352)	(50,225)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of 1,468, 13,120, 87,959 and 105,542 shares of common stock for 3 months ended September 30, 2019 and 2020 and the 9 months ended September 30, 2019 and 2020, respectively	95	56			39
Issuance 1,786, 1,861, 5,821, and 5,430 shares of common stock under the employee stock purchase plan for 3 months ended September 30, 2019 and 2020 and the 9 months ended September 30, 2019 and 2020, respectively	102	102
Unearned restricted stock compensation	165	165
Forfeiture of 134, 3,188, 5,255 and 4,211 shares of common stock for 3 months ended September 30, 2019 and 2020 and the 9 months ended September 30, 2019 and 2020, respectively	(8)	(8)
Share-based compensation	6	6
Change related to ESOP shares	(1,077)					(1,077)
Net income	11,282		11,282
Purchase of 8,209, 29,807, 83,606 and 112,407 shares of common stock for 3 months ended September 30, 2019 and 2020 and the 9 months ended September 30, 2019 and 2020, respectively	(530)				(530)
Other comprehensive income	276			276
Ending Balance at Sep. 30, 2019	363,835	55,836	397,896	1,248	(39,843)	(51,302)
Beginning Balance at Dec. 31, 2019	375,211	55,943	409,509	1,415	(39,830)	(51,826)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of 1,468, 13,120, 87,959 and 105,542 shares of common stock for 3 months ended September 30, 2019 and 2020 and the 9 months ended September 30, 2019 and 2020, respectively	6,815	4,005			2,810
Issuance 1,786, 1,861, 5,821, and 5,430 shares of common stock under the employee stock purchase plan for 3 months ended September 30, 2019 and 2020 and the 9 months ended September 30, 2019 and 2020, respectively	304	304
Unearned restricted stock compensation	(81)	(81)
Forfeiture of 134, 3,188, 5,255 and 4,211 shares of common stock for 3 months ended September 30, 2019 and 2020 and the 9 months ended September 30, 2019 and 2020, respectively	(218)	(218)
Share-based compensation	19	19
Change related to ESOP shares	4,931					4,931
Net income	30,216		30,216
Cash dividends ($0.82 and $0.89 per share for 9 months ended September 30, 2019 and 2020, respectively)	(8,324)		(8,324)
Purchase of 8,209, 29,807, 83,606 and 112,407 shares of common stock for 3 months ended September 30, 2019 and 2020 and the 9 months ended September 30, 2019 and 2020, respectively	(7,230)				(7,230)
Other comprehensive income	5,616			5,616
Ending Balance at Sep. 30, 2020	407,259	59,972	431,401	7,031	(44,250)	(46,895)
Beginning Balance at Jun. 30, 2020	398,719	60,043	419,971	6,821	(42,787)	(45,329)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of 1,468, 13,120, 87,959 and 105,542 shares of common stock for 3 months ended September 30, 2019 and 2020 and the 9 months ended September 30, 2019 and 2020, respectively	809	458			351
Issuance 1,786, 1,861, 5,821, and 5,430 shares of common stock under the employee stock purchase plan for 3 months ended September 30, 2019 and 2020 and the 9 months ended September 30, 2019 and 2020, respectively	104	104
Unearned restricted stock compensation	(474)	(474)
Forfeiture of 134, 3,188, 5,255 and 4,211 shares of common stock for 3 months ended September 30, 2019 and 2020 and the 9 months ended September 30, 2019 and 2020, respectively	(166)	(166)
Share-based compensation	7	7
Change related to ESOP shares	(1,566)					(1,566)
Net income	11,430		11,430
Purchase of 8,209, 29,807, 83,606 and 112,407 shares of common stock for 3 months ended September 30, 2019 and 2020 and the 9 months ended September 30, 2019 and 2020, respectively	(1,814)				(1,814)
Other comprehensive income	210			210
Ending Balance at Sep. 30, 2020	$ 407,259	$ 59,972	$ 431,401	$ 7,031	$ (44,250)	$ (46,895)