Stock-Based Compensation Plans (Details Textual) (USD $)	3 Months Ended
	Mar. 31, 2012	Mar. 31, 2011
Additional Stock-based Compensation Plans (Textual) [Abstract]
Stock-based compensation cost	$ 2,894,000	$ 2,744,000
Cash received from option exercises and employee stock purchase plan purchases	1,300,000	900,000
Increase in financing activities and decrease in operating activities due to tax benefit relating to excess stock based compensation deductions	500,000	400,000
Income tax benefit for stock based compensation arrangements	$ 800,000	$ 800,000
Long Term Incentive Plan [Member]
Stock-based Compensation Plans (Textual) [Abstract]
Maximum number of shares available for issuance under the plan	7,500,000
Expiry date for stock options grant	March 8, 2017
Maximum period for exercise of outstanding option awards	over a period not to exceed ten years
Maximum period for vesting of outstanding option awards	over a period not to exceed five years
Shares available for granted under the incentive plan	1,070,540
Restricted Stock [Member] | Maximum [Member]
Stock-based Compensation Plans (Textual) [Abstract]
Range of forfeiture provisions	5 years
Restricted Stock [Member] | Minimum [Member]
Stock-based Compensation Plans (Textual) [Abstract]
Range of forfeiture provisions	6 months
Employee Stock Purchase Plan [Member]
Stock-based Compensation Plans (Textual) [Abstract]
Expiry date for stock options grant	After March 6, 2016
Shares authorized under Employee stock option plan	3,500,000
Employee stock purchase price in percentage of fair market value	85.00%
Shares remaining in reserve for future issuance	803,878
Shares issued to employee under purchase plan	27,163	23,298
Weighted average fair value of employee stock purchase rights issued	$ 12.96	$ 10.22