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	51,038		51,038
Other comprehensive income (loss)	2,635			2,635
Cash dividends declared :
Common stock at $0.79 per share in 2013 and $0.90 per share in 2012	(52,375)		(52,375)
Excess tax benefit on share-based compensation	417	417
Exercise of stock options, net of shares purchased (in shares)					71,391
Exercise of stock options, net of shares purchased	18	(1,193)			1,211
Restricted stock awards, net of forfeitures (in shares)					172,471
Restricted stock awards, net of forfeitures	(1,075)	(4,053)			2,978
Share-based compensation expense	3,087	3,087
Ending Balances at Sep. 30, 2012	715,966	578,129	330,014	(18,855)	(173,322)
Ending Balances (in shares) at Sep. 30, 2012		68,730,731			(10,219,815)
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	44,564		44,564
Other comprehensive income (loss)	(10,617)			(10,617)
Cash dividends declared :
Common stock at $0.79 per share in 2013 and $0.90 per share in 2012	(45,575)		(45,575)
Purchase of common stock, in shares					(540,400)
Purchase of common stock	(8,339)				(8,339)
Excess tax benefit on share-based compensation	133	133
Exercise of stock options, net of shares purchased (in shares)					44,105
Exercise of stock options, net of shares purchased	(275)	(1,016)			741
Restricted stock awards, net of forfeitures (in shares)					152,504
Restricted stock awards, net of forfeitures	(1,326)	(4,030)			2,704
Share-based compensation expense	3,049	3,049
Ending Balances at Sep. 30, 2013	$ 692,039	$ 577,429	$ 328,993	$ (29,294)	$ (185,089)
Ending Balances (in shares) at Sep. 30, 2013		68,730,731			(11,028,287)