Stock-Based Compensation Plans (Details Textual) (USD $)	3 Months Ended		9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013	Sep. 30, 2014	Sep. 30, 2013
Additional Stock-based Compensation Plans (Textual) [Abstract]
Cash received from option exercises and employee stock purchase plan purchases			$ 4,700,000	$ 4,400,000
Tax benefit realized for the tax deductions			1,100,000	1,400,000
Share-based Compensation	$ 4,000,000	$ 3,500,000	$ 11,871,000	$ 10,473,000
2007 Long Term Incentive Plan [Member]
Stock-based Compensation Plans (Textual) [Abstract]
Maximum number of shares available for issuance under the plan	7,500,000		7,500,000
2014 Long Term Incentive Plan [Member]
Stock-based Compensation Plans (Textual) [Abstract]
Maximum number of shares available for issuance under the plan	1,200,000		1,200,000
Expiry date for stock options grant	May 21, 2024
Shares available for granted under the incentive plan	1,750,584		1,750,584
Employee Stock Purchase Plan [Member]
Stock-based Compensation Plans (Textual) [Abstract]
Expiry date for stock options grant			Mar. 06, 2016
Shares authorized for issuance	3,500,000		3,500,000
Employee stock purchase price in percentage of fair market value	85.00%
Shares remaining in reserve for future issuance	539,026		539,026
Shares issued to employee under purchase plan	80,938	83,698
Weighted average fair value of employee stock purchase rights issued	$ 15.07	$ 13.65
Maximum [Member]
Stock-based Compensation Plans (Textual) [Abstract]
Range Of Forfeiture Provisions			5 years