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, 2017	$ 311,716	$ 48,930	$ 341,558	$ (2,446)	$ (33,018)	$ (43,308)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of 88,943 and 84,164 shares of common stock for 3 months ended March 31, 2018 and 2019, respectively	4,804	2,580			2,224
Issuance 1,957 and 1,929 shares of common stock under the employee stock purchase plan for 3 months ended March 31, 2018 and 2019, respectively	100	100
Unearned restricted stock compensation	118	118
Forfeiture of 208 and 703 shares of common stock for 3 months ended March 31, 2018 and 2019, respectively		(8)
Change related to ESOP shares	(2,471)					(2,471)
Net income	10,858		10,858
Cash dividends ($0.75 and $0.82 per share for 3 months ended March 31, 2018 and 2019, respectively)	(7,002)		(7,002)
Reclassification of stranded tax effects due to the Tax Cuts and Jobs Act			526	(526)
Purchase of 47,432 and 69,771 shares of common stock for 3 months ended March 31, 2018 and 2019, respectively	(2,694)				(2,694)
Other comprehensive income (loss)	(903)			(903)
Ending Balance at Mar. 31, 2018	314,518	51,720	345,940	(3,875)	(33,488)	(45,779)
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 88,943 and 84,164 shares of common stock for 3 months ended March 31, 2018 and 2019, respectively	5,134	2,932			2,202
Issuance 1,957 and 1,929 shares of common stock under the employee stock purchase plan for 3 months ended March 31, 2018 and 2019, respectively	105	105
Unearned restricted stock compensation	170	170
Forfeiture of 208 and 703 shares of common stock for 3 months ended March 31, 2018 and 2019, respectively	(34)	(34)
Change related to ESOP shares	(981)					(981)
Net income	11,203		11,203
Cash dividends ($0.75 and $0.82 per share for 3 months ended March 31, 2018 and 2019, respectively)	(7,657)		(7,657)
Purchase of 47,432 and 69,771 shares of common stock for 3 months ended March 31, 2018 and 2019, respectively	(4,291)				(4,291)
Other comprehensive income (loss)	2,249			2,249
Ending Balance at Mar. 31, 2019	$ 340,780	$ 55,295	$ 375,394	$ (1,001)	$ (39,057)	$ (49,851)