CONSOLIDATED STATEMENTS OF CHANGES IN STOCKHOLDERS' EQUITY - 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, 2016		$ 412,726	$ 11,407	$ 126,462	$ (16,717)	$ (2,846)	$ 531,032
Net income				19,563			19,563
Other comprehensive loss, net of tax						(365)	(365)
Cash dividends declared on common stock ($0.150 per share)				(4,847)			(4,847)
Stock issuance costs		(180)					(180)
Exercise of stock options (10,846 and 46,497 shares)			118				118
Restricted stock grants (56,164 and 23,018 shares)
Stock-based compensation expense			852				852
Balance at Jun. 30, 2017		412,546	12,377	141,178	(16,717)	(3,211)	546,173
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 loss, net of tax						(3,974)	(3,974)
Cash dividends declared on common stock ($0.150 per share)				(4,838)			(4,838)
Stock issuance costs
Exercise of stock options (10,846 and 46,497 shares)			252				252
Restricted stock grants (56,164 and 23,018 shares)
Net performance units issued (42,672 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