CONSOLIDATED STATEMENTS OF CHANGES IN STOCKHOLDERS' EQUITY (unaudited) - USD ($) $ in Thousands	Preferred Stock [Member]	Common Stock [Member]	Additional Paid-In Capital [Member]	Retained Earnings [Member]	Treasury Stock [Member]	Accumulated Other Comprehensive (Loss) Income [Member]	Total
Balance at Dec. 31, 2017		$ 412,546	$ 13,602	$ 160,025	$ (16,717)	$ (4,019)	$ 565,437
Reclassification of stranded tax effects (ASU 2018-02) (see Note 8)				709		(709)
Cumulative effect of adopting ASU 2016-01 (see Note 8)				(55)		55
Net income				21,778			21,778
Other comprehensive income, net of tax						(3,974)	(3,974)
Cash dividends declared on common stock ($0.18 per share)				(4,838)			(4,838)
Exercise of stock options			252				252
Restricted stock grants
Net performance units issued (26,517 shares)			(819)				(819)
Stock-based compensation expense			721				721
Balance at Jun. 30, 2018		412,546	13,756	177,619	(16,717)	(8,647)	578,557
Balance at Mar. 31, 2018		412,546	13,434	162,510	(16,717)	(7,507)	564,266
Net income				17,108			17,527
Other comprehensive income, net of tax						(1,140)	(1,140)
Cash dividends declared on common stock ($0.18 per share)				(1,999)			(1,999)
Exercise of stock options			50				50
Restricted stock grants
Stock-based compensation expense			272				272
Balance at Jun. 30, 2018		412,546	13,756	177,619	(16,717)	(8,647)	578,557
Balance at Dec. 31, 2018		412,546	15,542	211,345	(16,717)	(8,789)	613,927
Net income				30,916			30,916
Other comprehensive income, net of tax						5,908	5,908
Cash dividends declared on common stock ($0.18 per share)				(6,612)			(6,612)
Exercise of stock options			265				265
Restricted stock grants
Repurchase of treasury stock (240,018 shares)					(5,175)		(5,175)
Net performance units issued (26,517 shares)			196				196
Stock issued (3,032,496 shares) in acquisition of Greater Hudson Bank		56,025					56,025
Restricted stock issued (119,008 shares) in acquisition of BoeFly LLC			2,500				2,500
Stock-based compensation expense			1,274				1,274
Balance at Jun. 30, 2019		468,571	19,777	235,649	(21,892)	(2,881)	699,224
Balance at Mar. 31, 2019		468,571	16,513	219,558	(16,967)	(5,280)	682,395
Net income				19,281			19,281
Other comprehensive income, net of tax						2,399	2,399
Cash dividends declared on common stock ($0.18 per share)				(3,190)			(3,190)
Exercise of stock options			122				122
Restricted stock grants
Repurchase of treasury stock (240,018 shares)					(4,925)		(4,925)
Stock issued (119,008 shares) in acquisition of BoeFly LLC			2,500				2,500
Stock-based compensation expense			642				642
Balance at Jun. 30, 2019		$ 468,571	$ 19,777	$ 235,649	$ (21,892)	$ (2,881)	$ 699,224