Consolidated Statements of Shareholders' Equity (USD $) In Thousands	Total	Common Stock	Retained Earnings
Balance at Dec. 31, 2009	$ 267,413	$ 50,869	$ 216,544
Balance, Shares at Dec. 31, 2009		23,795
Net Income	36,479		36,479
Non-Cash Stock-Based Compensation	4,227	4,227
Common Stock Issued under Stock Plans, net of Shares Withheld for Employee Taxes	7,506	7,506
Common Stock Issued under Stock Plans, net of Shares Withheld for Employee Taxes, Shares		440
Excess Tax Benefit from Equity Awards	1,021	1,021
Dividends Accrued of $0.90, $0.92, and $0.94 Per Share in 2010, 2011 and 2012 respectively	(21,669)		(21,669)
Balance at Dec. 31, 2010	294,977	63,623	231,354
Balance, Shares at Dec. 31, 2010		24,235
Net Income	49,602		49,602
Non-Cash Stock-Based Compensation	5,221	5,221
Common Stock Issued under Stock Plans, net of Shares Withheld for Employee Taxes	5,054	5,054
Common Stock Issued under Stock Plans, net of Shares Withheld for Employee Taxes, Shares		341
Excess Tax Benefit from Equity Awards	980	980
Dividends Accrued of $0.90, $0.92, and $0.94 Per Share in 2010, 2011 and 2012 respectively	(22,692)		(22,692)
Balance at Dec. 31, 2011	333,142	74,878	258,264
Balance, Shares at Dec. 31, 2011	24,576	24,576
Net Income	44,777		44,777
Non-Cash Stock-Based Compensation	3,840	3,840
Common Stock Issued under Stock Plans, net of Shares Withheld for Employee Taxes	5,591	5,591
Common Stock Issued under Stock Plans, net of Shares Withheld for Employee Taxes, Shares		355
Excess Tax Benefit from Equity Awards	1,033	1,033
Dividends Accrued of $0.90, $0.92, and $0.94 Per Share in 2010, 2011 and 2012 respectively	(23,645)		(23,645)
Balance at Dec. 31, 2012	$ 364,738	$ 85,342	$ 279,396
Balance, Shares at Dec. 31, 2012	24,931	24,931