Consolidated Statements of Changes in Stockholders' Equity - USD ($) $ in Thousands	Common Stock [Member]	Additional Paid-in Capital [Member]	Treasury Stock [Member]	Retained Earnings [Member]	AOCI Attributable to Parent [Member]	Total
Balance at Dec. 31, 2017	$ 315	$ 217,906	$ (57,675)	$ 381,048	$ (8,986)	$ 532,608
Reclassification of the Income Tax Effects of the Tax Cuts and Jobs Act from Accumulated Other Comprehensive Income (Loss) to Retained Earnings	0	0	0	2,073	(2,073)	2,073
Impact of adoption of Accounting Standard Update 2016-01	0	0	0	(779)	779
Net income	0	0	0	55,090	0	55,090
Award of common shares released from Employee Benefit Trust	0	2,728	0	0	0	2,728
Vesting of restricted stock unit awards	0	(4,929)	5,104	(175)	0
Exercise of stock options	0	(1)	10	(3)	0	6
Stock-based compensation expense	0	7,016	0	0	0	7,016
Purchase of treasury shares	0	0	(20,438)	0	0	(20,438)
Repurchase of shares to satisfy tax obligation	0	0	(2,147)	0	0	(2,147)
Dividends on common stock	0	0	0	(22,927)	0	(22,927)
Other comprehensive income (loss)	0	0	0	0	(2,472)	(2,472)
Balance at Dec. 31, 2018	315	222,720	(75,146)	414,327	(12,752)	549,464
Impact of Adoption of Accounting Standards Update	0	0	0	2,716	0	2,716
Net income	0	0	0	41,279	0	41,279
Award of common shares released from Employee Benefit Trust	0	2,307	0	0	0	2,307
Vesting of restricted stock unit awards	0	(6,099)	6,309	(210)	0
Exercise of stock options	0	0	6	(3)	0	3
Stock-based compensation expense	0	7,763	0	0	0	7,763
Purchase of treasury shares	0	0	(771)	0	0	(771)
Repurchase of shares to satisfy tax obligation	0	0	(1,885)	0	0	(1,885)
Dividends on common stock	0	0	0	(24,149)	0	(24,149)
Other comprehensive income (loss)	0	0	0	0	2,945	2,945
Balance at Dec. 31, 2019	315	226,691	(71,487)	433,960	(9,807)	579,672
Impact of adoption of Accounting Standard Update 2016-01	0	0	0	(875)	0	(875)
Net income	0	0	0	34,674	0	34,674
Shares issued in acquisition of Empire Bancorp, Inc.	26	32,679	0	0	0	32,705
Award of common shares released from Employee Benefit Trust	0	1,520	0	0	0	1,520
Vesting of restricted stock unit awards	0	(5,807)	5,964	(157)	0	0
Stock-based compensation expense	0	6,450	0	0	0	6,450
Purchase of treasury shares	0	0	(2,342)	0	0	(2,342)
Repurchase of shares to satisfy tax obligation	0	0	(1,535)	0	0	(1,535)
Dividends on common stock	0	0	0	(24,813)	0	(24,813)
Other comprehensive income (loss)	0	0	0	0	(6,459)	(6,459)
Balance at Dec. 31, 2020	$ 341	$ 261,533	$ (69,400)	$ 442,789	$ (16,266)	$ 618,997