CONSOLIDATED STATEMENTS OF CHANGES IN SHAREHOLDERS' EQUITY - USD ($) $ in Thousands	Total	Common Stock	Retained earnings	Accumulated other comprehensive income (loss)	Treasury stock
Beginning Balances (in shares) at Dec. 31, 2014		68,730,731			(7,274,184)
Beginning Balances at Dec. 31, 2014	$ 783,771	$ 574,643	$ 352,587	$ (21,409)	$ (122,050)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	36,570		36,570
Other comprehensive income (loss)	694			694
Cash dividends declared :
Common stock at $0.32 per share in 2016 and $0.32 per share in 2015	(19,695)		(19,695)
Excess tax benefit on share-based compensation	106	106
Exercise of stock options, net of shares purchased (in shares)					18,067
Exercise of stock options, net of shares purchased	129	(174)			$ 303
Restricted stock awards, net of forfeitures (in shares)					233,233
Restricted stock awards, net of forfeitures	(1,236)	(5,118)			$ 3,882
Share-based compensation expense	2,044	$ 2,044
Ending Balances (in shares) at Jun. 30, 2015		68,730,731			(7,022,884)
Ending Balances at Jun. 30, 2015	802,383	$ 571,501	369,462	(20,715)	$ (117,865)
Beginning Balances (in shares) at Dec. 31, 2015		68,730,731			(7,089,051)
Beginning Balances at Dec. 31, 2015	809,376	$ 571,155	388,240	(30,580)	$ (119,439)
Beginning Balance-Stockholders' Equity, Adjusted Balance at Dec. 31, 2015	809,376
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	42,382		42,382
Other comprehensive income (loss)	12,892			12,892
Cash dividends declared :
Common stock at $0.32 per share in 2016 and $0.32 per share in 2015	(19,729)		(19,729)
Adjustments to Additional Paid in Capital, Other	0	(971)			$ 971
Stock Issued During Period, Shares, Other					57,575
Excess tax benefit on share-based compensation	156	156
Exercise of stock options, net of shares purchased (in shares)					45,928
Exercise of stock options, net of shares purchased	597	(177)			$ 774
Restricted stock awards, net of forfeitures (in shares)					214,346
Restricted stock awards, net of forfeitures	(1,347)	(4,872)			$ 3,525
Share-based compensation expense	2,396	$ 2,396
Ending Balances (in shares) at Jun. 30, 2016		68,730,731			(6,771,202)
Ending Balances at Jun. 30, 2016	$ 846,723	$ 567,687	$ 410,893	$ (17,688)	$ (114,169)