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				41,680			41,680
Other comprehensive income (loss), net of tax						(6,011)	(6,011)
Cash dividends declared on common stock ($0.27 per share)				(7,258)			(7,258)
Exercise of stock options (28,937 shares)			524				524
Net performance units issued (26,517 shares)			(819)				(819)
Stock-based compensation expense			1,318				1,318
Balance at Sep. 30, 2018		412,546	14,625	195,101	(16,717)	(10,684)	594,871
Balance at Jun. 30, 2018		412,546	13,756	177,619	(16,717)	(8,647)	578,557
Net income				19,902			19,902
Other comprehensive income (loss), net of tax						(2,037)	(2,037)
Cash dividends declared on common stock ($0.27 per share)				(2,420)			(2,420)
Exercise of stock options (28,937 shares)			272				272
Stock-based compensation expense			597				597
Balance at Sep. 30, 2018		412,546	14,625	195,101	(16,717)	(10,684)	594,871
Balance at Dec. 31, 2018		412,546	15,542	211,345	(16,717)	(8,789)	613,927
Net income				52,612			52,612
Other comprehensive income (loss), net of tax						7,661	7,661
Cash dividends declared on common stock ($0.27 per share)				(9,798)			(9,798)
Exercise of stock options (28,937 shares)			265				265
Repurchase of 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			1,947				1,947
Balance at Sep. 30, 2019		468,571	20,450	254,159	(21,892)	(1,128)	720,160
Balance at Jun. 30, 2019		468,571	19,777	235,649	(21,892)	(2,881)	699,224
Net income				21,696			21,696
Other comprehensive income (loss), net of tax						1,753	1,753
Cash dividends declared on common stock ($0.27 per share)				(3,186)			(3,186)
Stock-based compensation expense			673				673
Balance at Sep. 30, 2019		$ 468,571	$ 20,450	$ 254,159	$ (21,892)	$ (1,128)	$ 720,160