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Stock-Based Compensation Plans (Narrative) (Details)
3 Months Ended 9 Months Ended
Sep. 30, 2018
USD ($)
plan
shares
Sep. 30, 2017
USD ($)
Sep. 30, 2018
USD ($)
plan
shares
Sep. 30, 2017
USD ($)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Compensation expense for share-based payments | $ $ 4,829,463 $ 3,067,076 $ 13,196,413 $ 9,957,687
Compensation cost capitalized as part of inventory | $     $ 224,025 279,102
Employee Stock Option Plan        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Number of shares available for grant (in shares) | shares 24,000,000   24,000,000  
Unrecognized compensation cost | $ $ 9,600,422   $ 9,600,422  
Employee Stock Option Plan | Minimum        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Option vesting period     1 year  
Option expiration period     5 years  
Employee Stock Option Plan | Maximum        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Option vesting period     5 years  
Option expiration period     10 years  
Non Employee Director Stock Option Plan        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Option vesting period     6 months  
Option expiration period     10 years  
Unrecognized compensation cost | $ $ 87,458   $ 87,458  
Number of shares authorized (in shares) | shares 1,000,000   1,000,000  
Options granted (in shares) | shares     480,430  
Employee Stock Purchase Plan        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Shares approved (in shares) | shares 2,000,000   2,000,000  
ESPP discount rate     85.00%  
ESPP discount rate recognized as compensation expense     15.00%  
Shares granted (in shares) | shares 924,878   924,878  
Restricted Stock Plan        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Number of shares authorized (in shares) | shares 9,000,000   9,000,000  
Restricted period, maximum, in years     10 years  
Unearned stock-based compensation | $ $ 33,559,239   $ 33,559,239  
Amortization expense | $ $ 2,480,911 $ 1,788,162 $ 6,314,544 $ 4,014,820
Equity Incentive Plans        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Number of plans | plan 4   4  
Stock Options        
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]        
Number of plans | plan 2   2