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Stock-Based Compensation Plans (Narrative) (Details) |  |  | 12 Months Ended |  |  |
--- | --- | --- | --- | --- | --- | ---
Dec. 31, 2014 | Dec. 05, 2014 | Dec. 31, 2016 USD ($) plan $ / shares shares | Dec. 31, 2015 USD ($) $ / shares shares | Dec. 31, 2014 USD ($) $ / shares shares | May 31, 2014 shares | Dec. 31, 2012 shares | Dec. 31, 2003 shares
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |  |  |
Unrecognized compensation cost | $ |  |  | $ 0 |  |  |  |  |
Shares granted with restriction period (in shares) |  |  | 246,660 | 229,660 | 431,880 |  |  |
Employee Stock Option Plan |  |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |  |  |
Options available for grant (in shares) |  |  |  |  |  | 24,000,000 |  |
Options granted net of shares from canceled/expired options (in shares) |  |  | 10,342,260 |  |  |  |  |
Unrecognized compensation cost | $ |  |  | $ 17,732,000 |  |  |  |  |
Weighted-average period for unrecognized compensation cost expected to be recognized |  |  | 2 years |  |  |  |  |
Non-Employee Director Stock Option Plan |  |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |  |  |
Option vesting period |  |  | 6 months |  |  |  |  |
Shares approved (in shares) |  |  |  |  |  |  | 1,000,000 |
Grants in period (in shares) |  |  | 1,074,480 |  |  |  |  |
Option expiration period, years |  |  | 10 years |  |  |  |  |
Previous Non-Employee Director Stock Option Plan |  |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |  |  |
Grants in period (in shares) |  |  | 371,000 |  |  |  |  |
Restricted Stock Plan |  |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |  |  |
Shares approved (in shares) |  |  |  | 9,000,000 |  |  |  |
Restricted period, maximum, in years |  |  |  | 10 years |  |  |  |
Shares granted with restriction period (in shares) |  |  | 1,532,480 |  |  |  |  |
Shares, Granted (in shares) |  |  | 4,477,580 |  |  |  |  |
Restricted period for granted shares, in years |  |  | 5 years |  |  |  |  |
Unearned stock-based compensation | $ |  |  | $ 11,063,638 |  |  |  |  |
Amortization expense | $ |  |  | $ 3,885,042 | $ 3,486,242 | $ 3,095,136 |  |  |
Employee Stock Purchase Plan |  |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |  |  |
Shares approved (in shares) |  |  |  |  |  |  |  | 2,000,000
ESPP discount rate |  |  | 85.00% |  |  |  |  |
Discount recognized as compensation expense |  |  |  | 15.00% |  |  |  |
Employee Stock Purchase Plan, 2013 |  |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |  |  |
Shares sold to employees during period (in shares) |  |  | 177,781 | 201,785 | 137,028 |  |  |
Cumulative shares sold to employees during period (in shares) |  |  | 619,518 |  |  |  |  |
Weighted average fair value of shares sold (in dollars per share) | $ / shares |  |  | $ 14.24 |  |  |  |  |
Minimum | Employee Stock Option Plan |  |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |  |  |
Option vesting period |  |  | 1 year |  |  |  |  |
Award expiration period |  |  | 5 years |  |  |  |  |
Minimum | Restricted Stock Plan |  |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |  |  |
Market price (in dollars per share) | $ / shares |  |  | $ 14.70 | $ 15.50 | $ 13.39 |  |  |
Maximum | Employee Stock Option Plan |  |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |  |  |
Option vesting period |  |  | 5 years |  |  |  |  |
Award expiration period |  |  | 7 years |  |  |  |  |
Maximum | Restricted Stock Plan |  |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |  |  |
Market price (in dollars per share) | $ / shares |  |  | $ 19.69 | $ 18.30 | $ 18.31 |  |  |
Stock Compensation Plan [Member] |  |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |  |  |
Number of plans | plan |  |  | 4 |  |  |  |  |
Employee Stock Option [Member] |  |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |  |  |
Number of plans | plan |  |  | 2 |  |  |  |  |
Common Stocks |  |  |  |  |  |  |  |
Share-based Compensation Arrangement by Share-based Payment Award [Line Items] |  |  |  |  |  |  |  |
Common stock split conversion ratio | 2 | 2 |  |  |  |  |  |
Common stock split, stock dividend percent | 100.00% | 100.00% |  |  |  |  |  |

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