Statements Of Shareholders' Equity (USD $) Share data in Thousands, unless otherwise specified	Common Stock [Member]	Additional Paid-in Capital [Member]	Accumulated Other Comprehensive Income (Loss) [Member]	Retained Earnings [Member]	Treasury Stock [Member]	Total
Balance at Dec. 31, 2008	$ 481,000	$ 151,245,000	$ (387,000)	$ 50,494,000	$ (87,571,000)	$ 114,262,000
Balance, shares at Dec. 31, 2008	48,148				(12,333)
Comprehensive income:
Net income				27,010,000		27,010,000
Unrealized gain (loss) on investment securities, net of tax			(18,000)			(18,000)
Total comprehensive income						26,992,000
Issuance of shares pursuant to stock compensation plan		(3,774,000)			6,069,000	2,295,000
Issuance of shares pursuant to stock compensation plan, shares					425	425
Stock compensation		5,045,000				5,045,000
Treasury stock purchases					(17,000,000)	(17,000,000)
Treasury stock purchases, shares					(1,235)	(1,235)
Issuance of shares pursuant to Employee Stock Purchase Plan		(118,000)			1,546,000	1,428,000
Issuance of shares pursuant to Employee Stock Purchase Plan, shares					115	115
Federal income tax benefit related to exercise of stock options		1,336,000				1,336,000
Balance at Dec. 31, 2009	481,000	153,734,000	(405,000)	77,504,000	(96,956,000)	134,358,000
Balance, shares at Dec. 31, 2009	48,148				(13,028)
Comprehensive income:
Net income				25,054,000		25,054,000
Unrealized gain (loss) on investment securities, net of tax			130,000			130,000
Total comprehensive income						25,184,000
Issuance of shares pursuant to stock compensation plan		(8,157,000)			11,338,000	3,181,000
Issuance of shares pursuant to stock compensation plan, shares					615	615
Stock compensation		6,132,000				6,132,000
Treasury stock purchases					(65,793,000)	(65,793,000)
Treasury stock purchases, shares					(3,559)	(3,559)
Issuance of shares pursuant to Employee Stock Purchase Plan		(218,000)			2,043,000	1,825,000
Issuance of shares pursuant to Employee Stock Purchase Plan, shares					118	118
Federal income tax benefit related to exercise of stock options		2,085,000				2,085,000
Balance at Dec. 31, 2010	481,000	153,576,000	(275,000)	102,558,000	(149,368,000)	106,972,000
Balance, shares at Dec. 31, 2010	48,148				(15,854)
Comprehensive income:
Net income				27,557,000		27,557,000
Unrealized gain (loss) on investment securities, net of tax			(80,000)			(80,000)
Total comprehensive income						27,477,000
Issuance of shares pursuant to stock compensation plan		(10,352,000)			13,905,000	3,553,000
Issuance of shares pursuant to stock compensation plan, shares					582	582
Stock compensation		6,253,000				6,253,000
Treasury stock purchases					(71,802,000)	(71,802,000)
Treasury stock purchases, shares					(3,004)	(3,004)
Issuance of shares pursuant to Employee Stock Purchase Plan		(230,000)			2,275,000	2,045,000
Issuance of shares pursuant to Employee Stock Purchase Plan, shares					100	100
Federal income tax benefit related to exercise of stock options		3,612,000				3,612,000
Balance at Dec. 31, 2011	$ 481,000	$ 152,859,000	$ (355,000)	$ 130,115,000	$ (204,990,000)	$ 78,110,000
Balance, shares at Dec. 31, 2011	48,148				(18,176)