Consolidated Statements Of Stockholders' Equity (Unaudited) (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, 2014	$ 275,830		$ 729	$ 186,022	$ 25	$ 100,237	$ (11,183)
Balance (in shares) at Dec. 31, 2014			72,878
Comprehensive income:
Net income for the period	15,516					15,516
Unrealized gain on available for sale marketable securities, net of taxes	3	[1]			3
Total comprehensive income	15,519
Exercise of stock options, net of shares tendered for payment (in shares)			164
Exercise of stock options, net of shares tendered for payment	2,884		1	2,883
Tax benefit from equity compensation plans	499			499
Share-based compensation expense — stock options and restricted stock	777			777
Treasury shares issued for Deferred Compensation Plan funding and redemptions	491			443			48
Shares issued pursuant to Employee Stock Purchase Plan	1,701			1,363			338
Cash dividends	(12,655)					(12,655)
Shares issued pursuant to Dividend Reinvestment Plan	26			83			(57)
Shares issued pursuant to prior year acquisition (in shares)			176
Shares issued pursuant to prior year acquisition	0		2	(2)
Balance at Mar. 31, 2015	$ 285,072		$ 732	$ 192,068	$ 28	$ 103,098	$ (10,854)
Balance (in shares) at Mar. 31, 2015			73,218

[1] All amounts are net of tax.