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, 2013	$ 285,143		$ 719	$ 168,329	$ 49	$ 127,464	$ (11,418)
Balance (in shares) at Dec. 31, 2013			71,868
Comprehensive income:
Net income for the period	28,560					28,560
Unrealized gain on available for sale marketable securities, net of taxes	7	[1]			7
Total comprehensive income	28,567
Exercise of stock options, net of shares tendered for payment	3,834		2	3,832
Exercise of stock options and other stock-based compensation, net of shares tendered for payment (in shares)			270
Tax benefit from equity compensation plans	885			885
Share-based compensation expense — stock options and restricted stock	1,350			1,350
Treasury shares issued for Deferred Compensation Plan funding and redemptions	518			513			5
Shares issued pursuant to Employee Stock Purchase Plan	1,851			1,457			394
Cash dividends	(24,263)					(24,263)
Shares issued pursuant to Dividend Reinvestment Plan	28			141			(113)
Adjustment to purchase price allocation	3,934			3,934
Balance at Jun. 30, 2014	$ 301,847		$ 721	$ 180,441	$ 56	$ 131,761	$ (11,132)
Balance (in shares) at Jun. 30, 2014			72,138

[1] All amounts are net of tax.