Consolidated Statements Of Stockholders' Equity (USD $) In Thousands, unless otherwise specified	Total		Common Stock [Member]	Additional Paid-In Capital [Member]	Accumulated Other Comprehensive Income [Member]	Retained Earnings [Member]	Treasury Stock [Member]
Balance at Dec. 31, 2011	$ 217,726		$ 695	$ 105,727	$ 343	$ 126,921	$ (15,960)
Balance (in shares) at Dec. 31, 2011			69,473
Comprehensive income:
Net income for the period	44,214					44,214
Unrealized loss on available for sale marketable securities, net of taxes	(216)				(216)
Total comprehensive income	43,998
Exercise of stock options and other stock-based compensation, net of shares tendered for payment	5,573		5	4,098			1,470
Exercise of stock options and other stock-based compensation, net of shares tendered for payment (in shares)			563
Tax benefit from equity compensation plans	2,649			2,649
Share-based compensation expense — stock options and restricted stock	1,897			1,897
Treasury shares issued for Deferred Compensation Plan funding and redemptions	453			394			59
Shares issued pursuant to Employee Stock Plans	1,249			1,278			(29)
Cash dividends	(44,093)					(44,093)
Shares issued pursuant to Dividend Reinvestment Plan	118			85			33
Shares issued pursuant to current year acquisition	0			(2,633)			2,633
Balance at Dec. 31, 2012	229,570		700	113,495	127	127,042	(11,794)
Balance (in shares) at Dec. 31, 2012			70,036
Comprehensive income:
Net income for the period	47,129					47,129
Unrealized loss on available for sale marketable securities, net of taxes	(78)				(78)
Total comprehensive income	47,051
Exercise of stock options and other stock-based compensation, net of shares tendered for payment	6,428		7	6,381			40
Exercise of stock options and other stock-based compensation, net of shares tendered for payment (in shares)			617
Tax benefit from equity compensation plans	2,615			2,615
Share-based compensation expense — stock options and restricted stock	2,045			2,045
Treasury shares issued for Deferred Compensation Plan funding and redemptions	360			294			66
Shares issued pursuant to Employee Stock Plans	1,842			1,370			472
Cash dividends	(46,707)					(46,707)
Shares issued pursuant to Dividend Reinvestment Plan	107			309			(202)
Shares issued pursuant to current year acquisition	41,832		12	41,820			0
Shares issued pursuant to acquisition (in shares)			1,215
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	21,850					21,850
Unrealized loss on available for sale marketable securities, net of taxes	(24)	[1]			(24)
Total comprehensive income	21,826
Exercise of stock options and other stock-based compensation, net of shares tendered for payment	6,196		5	6,191
Exercise of stock options and other stock-based compensation, net of shares tendered for payment (in shares)			534
Tax benefit from equity compensation plans	2,626			2,626
Share-based compensation expense — stock options and restricted stock	2,705			2,705
Treasury shares issued for Deferred Compensation Plan funding and redemptions	516			459			57
Shares issued pursuant to Employee Stock Plans	1,851			1,457			394
Cash dividends	(49,077)					(49,077)
Shares issued pursuant to Dividend Reinvestment Plan	110			326			(216)
Adjustment to Paid in Capital, Purchase Price Allocation Adjustment	3,934			3,934
Shares issued pursuant to current year acquisition	0		5	(5)
Shares issued pursuant to acquisition (in shares)			476
Balance at Dec. 31, 2014	$ 275,830		$ 729	$ 186,022	$ 25	$ 100,237	$ (11,183)
Balance (in shares) at Dec. 31, 2014			72,878

[1] All amounts are net of tax.