CONSOLIDATED STATEMENTS OF CHANGES IN SHAREHOLDERS' EQUITY (USD $) In Thousands, except Share data, unless otherwise specified	Total	Common Stock	Retained earnings	Accumulated other comprehensive income (loss)	Treasury stock
Beginning Balances at Dec. 31, 2013	$ 682,161	$ 577,076	$ 324,192	$ (31,281)	$ (187,826)
Beginning Balances (in shares) at Dec. 31, 2013		68,730,731			(11,197,685)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	15,104		15,104
Other comprehensive income (loss)	3,633			3,633
Cash dividends declared :
Common stock at $0.16 per share in 2015 and $0.15 per share in 2014	(8,624)		(8,624)
Purchase of common stock, in shares					(40,255)
Purchase of common stock	(697)				(697)
Excess tax benefit on share-based compensation	254	254
Exercise of stock options, net of shares purchased (in shares)					33,794
Exercise of stock options, net of shares purchased	(139)	(703)			564
Restricted stock awards, net of forfeitures (in shares)					183,352
Restricted stock awards, net of forfeitures	(1,155)	(4,194)			3,039
Share-based compensation expense	810	810
Ending Balances at Mar. 31, 2014	691,347	573,243	330,672	(27,648)	(184,920)
Ending Balances (in shares) at Mar. 31, 2014		68,730,731			(11,020,794)
Beginning Balance-Stockholders' Equity, Adjusted Balance at Dec. 31, 2014	783,771
Beginning Balances at Dec. 31, 2014	784,077	574,643	352,587	(21,409)	(122,050)
Beginning Balances (in shares) at Dec. 31, 2014		68,730,731			(7,274,184)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	17,621		17,621
Other comprehensive income (loss)	4,355			4,355
Cash dividends declared :
Common stock at $0.16 per share in 2015 and $0.15 per share in 2014	(9,818)		(9,818)
Excess tax benefit on share-based compensation	99	99
Exercise of stock options, net of shares purchased (in shares)					15,217
Exercise of stock options, net of shares purchased	86	(170)			256
Restricted stock awards, net of forfeitures (in shares)					215,123
Restricted stock awards, net of forfeitures	(1,230)	(4,807)			3,577
Share-based compensation expense	858	858
Ending Balances at Mar. 31, 2015	$ 795,742	$ 570,623	$ 360,390	$ (17,054)	$ (118,217)
Ending Balances (in shares) at Mar. 31, 2015		68,730,731			(7,043,844)