Consolidated Statements of Changes in Stockholders' Equity - USD ($) $ in Thousands	Total	Common Stock	Additional Paid-in Capital	Unallocated Common Stock Held by the Employee Stock Ownership Plan	Retained Earnings	Accumulated Other Comprehensive Income (loss) Net of tax	Treasury Stock
Beginning Balance (in shares) at Dec. 31, 2016		48,526,658
Beginning Balance at Dec. 31, 2016	$ 621,196	$ 609	$ 547,910	$ (23,466)	$ 268,226	$ (4,332)	$ (167,751)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	24,768				24,768
Other comprehensive loss, net of tax	(227)					(227)
Reclassification of tax effects resulting from the adoption of ASU No. 2018-02 | ASU 2018-02	0				892	(892)
Employee Stock Ownership Plan (ESOP) shares allocated or committed to be released	2,489		1,267	1,222
Stock compensation expense	6,197		6,197
Additional tax benefit on equity awards	0
Net issuance of restricted stock (in shares)		(58,447)
Net issuance of restricted stock	0		828				(828)
Exercise of stock options, net (in shares)		335,674
Exercise of stock options, net	100		(4,440)				4,540
Cash dividends declared	(15,646)				(15,646)
Ending Balance (in shares) at Dec. 31, 2017		48,803,885
Ending Balance at Dec. 31, 2017	638,877	$ 609	548,864	(22,244)	281,138	(5,451)	(164,039)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	40,079				40,079
Other comprehensive loss, net of tax	(3,696)					(3,696)
Employee Stock Ownership Plan (ESOP) shares allocated or committed to be released	2,337		1,085	1,252
Stock compensation expense	5,432		5,432
Net forfeitures of restricted stock (in shares)		10,040
Net forfeitures of restricted stock	$ 0		(133)				133
Exercise of stock options, net (in shares)	1,339,714	822,074
Exercise of stock options, net	$ 2,088		(9,029)				11,117
Cash dividends declared	(18,673)				(18,673)
Treasury stock (in shares)		(326)
Treasury stock	(5)						(5)
Ending Balance (in shares) at Dec. 31, 2018		49,635,673
Ending Balance at Dec. 31, 2018	666,439	$ 609	546,219	(20,992)	302,544	(9,147)	(152,794)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	40,235				40,235
Other comprehensive loss, net of tax	13,846					13,846
Employee Stock Ownership Plan (ESOP) shares allocated or committed to be released	2,340		1,088	1,252
Stock compensation expense	3,236		3,236
Net issuance of restricted stock (in shares)		(8,000)
Net issuance of restricted stock	$ 0		118				(118)
Exercise of stock options, net (in shares)	1,009,402	583,574
Exercise of stock options, net	$ 5,770		(2,175)				7,945
Cash dividends declared	(20,198)				(20,198)
Treasury stock (in shares)		(1,035,900)
Treasury stock	(15,815)						(15,815)
Ending Balance (in shares) at Dec. 31, 2019		49,175,347
Ending Balance at Dec. 31, 2019	$ 695,853	$ 609	$ 548,486	$ (19,740)	$ 322,581	$ 4,699	$ (160,782)