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, 2011	$ 712,221	$ 579,871	$ 331,351	$ (21,490)	$ (177,511)
Beginning Balances (in shares) at Dec. 31, 2011		68,730,731			(10,463,677)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	16,994		16,994
Other comprehensive income (loss)	2,803			2,803
Cash dividends declared :
Common stock at $0.28 per share in 2013 and $0.31 per share in 2012	(17,782)		(17,782)
Excess tax benefit on share-based compensation	283	283
Exercise of stock options, net of shares purchased (in shares)					47,169
Exercise of stock options, net of shares purchased	(25)	(825)			800
Restricted stock awards, net of forfeitures (in shares)					225,235
Restricted stock awards, net of forfeitures	(553)	(4,406)			3,853
Share-based compensation expense	752	752
Ending Balances at Mar. 31, 2012	714,693	575,675	330,563	(18,687)	(172,858)
Ending Balances (in shares) at Mar. 31, 2012		68,730,731			(10,191,273)
Beginning Balances at Dec. 31, 2012	710,425	579,293	330,004	(18,677)	(180,195)
Beginning Balances (in shares) at Dec. 31, 2012		68,730,731			(10,684,496)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	13,824		13,824
Other comprehensive income (loss)	(2,798)			(2,798)
Cash dividends declared :
Common stock at $0.28 per share in 2013 and $0.31 per share in 2012	(16,193)		(16,193)
Purchase of common stock, in shares					(249,000)
Purchase of common stock	(3,831)				(3,831)
Excess tax benefit on share-based compensation	73	73
Exercise of stock options, net of shares purchased (in shares)					20,370
Exercise of stock options, net of shares purchased	(136)	(479)			343
Restricted stock awards, net of forfeitures (in shares)					211,318
Restricted stock awards, net of forfeitures	(837)	(4,460)			3,623
Share-based compensation expense	1,087	1,087
Ending Balances at Mar. 31, 2013	$ 701,614	$ 575,514	$ 327,635	$ (21,475)	$ (180,060)
Ending Balances (in shares) at Mar. 31, 2013		68,730,731			(10,701,808)