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, 2010	$ 697,394	$ 580,097	$ 310,271	$ (12,044)	$ (180,930)
Beginning Balances (in shares) at Dec. 31, 2010		68,730,731			(10,665,754)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	48,798		48,798
Other comprehensive income	8,656			8,656
Cash dividends declared :
Common stock at $0.90 per share in 2012 and $0.51 per share in 2011	(29,826)		(29,826)
Excess tax benefit on share-based compensation	167	167
Exercise of stock options, net of shares purchased (in shares)					12,808
Exercise of stock options, net of shares purchased	(11)	(228)			217
Restricted stock awards, net of forfeitures (in shares)					178,351
Restricted stock awards, net of forfeitures	913	(3,929)			(3,016)
Share-based compensation expense	2,867	2,867
Ending Balances at Sep. 30, 2011	727,132	578,974	329,243	(3,388)	(177,697)
Ending Balances (in shares) at Sep. 30, 2011		68,730,731			(10,474,595)
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	2,635			2,635
Cash dividends declared :
Common stock at $0.90 per share in 2012 and $0.51 per share in 2011	(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)