Consolidated Statements of Changes in Shareholders’ Equity (Unaudited) (USD $) In Thousands	Common Stock [Member]	Accumulated Deferred Compensation [Member]	Accumulated Other Comprehensive Income (Loss) [Member]	Retained Earnings [Member]	Total
Beginning balance at Dec. 31, 2012	$ 372,012	$ 3,101	$ 14,625	$ 170,364	$ 560,102
Beginning balance (in Shares) at Dec. 31, 2012	27,213
Net income for the period				51,121	51,121
Other comprehensive income			(10,505)		(10,505)
Exercise of stock options	9,219				9,219
Exercise of stock options (in Shares)	221
Tax benefit increase (decrease) upon exercise of stock options	(202)				(202)
Restricted stock activity	1,068	(390)			678
Restricted stock activity (in Shares)	15
Stock based compensation	1,081				1,081
Stock awarded to employees	84				84
Stock awarded to employees (in Shares)	2
Purchase and retirement of stock	(12,174)			(27,615)	(39,789)
Purchase and retirement of stock (in Shares)	(873)
Dividends				(29,949)	(29,949)
Ending balance at Sep. 30, 2013	371,088	2,711	4,120	163,921	541,840
Ending balance (in Shares) at Sep. 30, 2013	26,578
Beginning balance at Dec. 31, 2013	378,946	2,711	4,313	156,964	542,934
Beginning balance (in Shares) at Dec. 31, 2013	26,510
Net income for the period				45,618	45,618
Other comprehensive income			5,420		5,420
Exercise of stock options	12,396				12,396
Exercise of stock options (in Shares)	256
Tax benefit increase (decrease) upon exercise of stock options	(447)				(447)
Restricted stock activity	1,114				1,114
Restricted stock activity (in Shares)	21
Stock based compensation	1,009				1,009
Stock awarded to employees	88				88
Stock awarded to employees (in Shares)	2
Purchase and retirement of stock	(12,911)			(31,899)	(44,810)
Purchase and retirement of stock (in Shares)	(883)
Dividends				(29,927)	(29,927)
Ending balance at Sep. 30, 2014	$ 380,195	$ 2,711	$ 9,733	$ 140,756	$ 533,395
Ending balance (in Shares) at Sep. 30, 2014	25,906