Quarterly report pursuant to Section 13 or 15(d)

Stock-based Expense (Details)

v3.8.0.1
Stock-based Expense (Details)
3 Months Ended
Mar. 31, 2018
$ / shares
shares
Restricted Stock | Vesting condition 4  
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]  
Granted shares of restricted stock (in shares) 129,341
Performance-Based Restricted Stock  
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]  
Granted shares of restricted stock (in shares) 517,364
Performance-Based Restricted Stock | Vesting condition 1  
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]  
Granted shares of restricted stock (in shares) 129,341
Number of consecutive trading days required to calculate average price per share (in days) 20 days
Minimum price per common stock for vesting eligibility (in dollars per share) | $ / shares $ 60.89
Performance-Based Restricted Stock | Vesting condition 2  
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]  
Granted shares of restricted stock (in shares) 129,341
Number of consecutive trading days required to calculate average price per share (in days) 20 days
Minimum price per common stock for vesting eligibility (in dollars per share) | $ / shares $ 66.98
Performance-Based Restricted Stock | Vesting condition 3  
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]  
Granted shares of restricted stock (in shares) 129,341
Number of consecutive trading days required to calculate average price per share (in days) 20 days
Minimum price per common stock for vesting eligibility (in dollars per share) | $ / shares $ 73.07
Performance-Based Restricted Stock | Vesting condition 4  
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]  
Number of consecutive trading days required to calculate average price per share (in days) 20 days
Minimum price per common stock for vesting eligibility (in dollars per share) | $ / shares $ 85.24
2010 Equity Incentive Plan | Restricted Stock | Vesting condition 1  
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]  
Granted shares of restricted stock (in shares) 814,678
Vesting period (in years) 3 years
2010 Equity Incentive Plan | Restricted Stock | Vesting condition 2  
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]  
Granted shares of restricted stock (in shares) 3,600
Vesting period (in years) 1 year