Consolidated Statements Of Stockholders' Equity (USD $) In Thousands, unless otherwise specified	Total		Common Stock [Member]	Additional Paid-In Capital [Member]	Accumulated Other Comprehensive Income, net of taxes [Member]	Retained Earnings [Member]	Treasury Stock [Member]
Balance at Dec. 31, 2012	$ 229,570		$ 700	$ 113,495	$ 127	$ 127,042	$ (11,794)
Balance, Shares at Dec. 31, 2012			70,036
Comprehensive income:
Net income for the period	41,677					41,677
Unrealized loss on available for sale marketable securities, net of taxes	(84)	[1]			(84)
Total comprehensive income	41,593
Exercise of stock options and other stock-based compensation, net of shares tendered for payment	5,469		5	5,424			40
Exercise of stock options and other stock-based compensation, net of shares tendered for payment, Shares			439
Tax benefit from equity compensation plans	1,355			1,355
Share-based compensation expense — stock options and restricted stock	1,529			1,529
Treasury shares issued for Deferred Compensation Plan funding and redemptions	361			350			11
Shares issued pursuant to Employee Stock Plans	1,842			1,370			472
Cash dividends	(34,760)					(34,760)
Shares issued pursuant to Dividend Reinvestment Plan	80			232			(152)
Shares issued pursuant to acquisition	41,832		12	41,820
Shares issued pursuant to acquisition (in shares)			1,215
Balance at Sep. 30, 2013	$ 288,871		$ 717	$ 165,575	$ 43	$ 133,959	$ (11,423)
Balance, Shares at Sep. 30, 2013			71,690

[1] All amounts are net of tax.