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Share-Based Compensation (Tables)
 9 Months Ended
Sep. 30, 2012
Disclosure of Compensation Related Costs, Share-based Payments [Abstract]  
Summary of stock option activity
 
Stock
Options
 
Weighted-
Average
Exercise
Price
Outstanding at December 31, 2011
3,776

 
$
16.92

Granted
462

 
$
18.94

Exercised
(225
)
 
$
14.78

Canceled
(52
)
 
$
14.84

Outstanding at September 30, 2012
3,961

 
$
17.25

Exercisable at September 30, 2012
2,828

 
$
17.27

Vested and expected to vest at September 30, 2012
3,931

 
$
17.26
Summary of nonvested stock activity
 
Shares    
 
Grant Date
Weighted-
Average Fair
Value
Per Share
Outstanding at December 31, 2011
1,516

 
$
20.76

Granted
69

 
$
21.41

Vested
(437
)
 
$
22.15

Forfeited/Canceled
(1
)
 
$
42.33

Outstanding at September 30, 2012
1,147

 
$
20.27
Schedule of Share-based Payment Award, Stock Options, Valuation Assumptions [Table Text Block]
The fair value of our options is estimated on the date of grant using the Black-Scholes option pricing model. We amortize the fair value of our options on a straight-line basis over the requisite service period. The following assumptions were used to determine the preliminary fair value of those options granted during the nine months ended September 30, 2012:
Expected volatility (1)
 
34.1
%
Weighted-average volatility (1)
 
34.1
%
Expected dividends
 
—

Expected term (years)
 
4.4

Risk-free rate (2)
 
0.62
%
_________________
(1)
We estimated the volatility of our common stock on the date of grant based on using both historical and implied volatilities.
(2)
The risk-free interest rate is based on the implied yield in effect at the time of option grant on U.S. Treasury zero-coupon issues with equivalent remaining terms.