Equity Compensation (Activity) (Details) - Stock options - $ / shares
|
|
12 Months Ended |
|
Jan. 01, 2018 |
Dec. 31, 2017 |
Dec. 31, 2016 |
Dec. 31, 2015 |
Jun. 11, 2013 |
| Shares Subject to Options Outstanding |
|
|
|
|
|
| Balance at the beginning of the period (in shares) |
2,069,802
|
3,776,405
|
4,572,672
|
4,851,221
|
|
| Exercised (in shares) |
|
(1,617,659)
|
(685,798)
|
(285,387)
|
|
| Expired (in shares) |
|
(60,275)
|
(76,907)
|
(47,866)
|
|
| Forfeited (in shares) |
|
(28,669)
|
(83,562)
|
(183,812)
|
|
| Balance at the end of the period (in shares) |
|
2,069,802
|
3,776,405
|
4,572,672
|
|
| Exercisable options (in shares) |
|
1,786,261
|
3,048,020
|
|
|
| Vested and expected to vest at the end of the period (in shares) |
|
2,069,802
|
3,733,643
|
|
|
| Weighted Average Grant Date Fair Value |
|
|
|
|
|
| Granted (in dollars per share) |
|
|
$ 4.63
|
$ 5.31
|
|
| Weighted Average Exercise Price |
|
|
|
|
|
| Balance at the beginning of the period (in dollars per share) |
$ 12.13
|
$ 11.55
|
10.72
|
10.57
|
|
| Granted (in dollars per share) |
|
|
8.16
|
10.52
|
|
| Exercised (in dollars per share) |
|
10.48
|
5.01
|
4.87
|
|
| Expired (in dollars per share) |
|
17.51
|
14.96
|
13.92
|
|
| Forfeited (in dollars per share) |
|
16.70
|
14.81
|
14.76
|
|
| Balance at the end of the period (in dollars per share) |
|
12.13
|
11.55
|
$ 10.72
|
|
| Exercisable options at the end of the period (in dollars per share) |
|
11.93
|
10.69
|
|
|
| Vested and expected to vest (in dollars per share) |
|
$ 12.13
|
$ 11.52
|
|
|
| Weighted-Average Remaining Contractual Life |
|
|
|
|
|
| Exercisable options |
|
5 years
|
5 years 4 months 24 days
|
|
|
| Vested and expected to vest |
|
5 years 3 months 18 days
|
5 years 9 months 18 days
|
|
|
| 2013 Plan |
|
|
|
|
|
| Stock options |
|
|
|
|
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| Potential annual increase in shares authorized for issuance as a percentage of shares outstanding as of the preceding December 31 |
|
|
|
|
5.00%
|
| 2013 Plan | Subsequent events |
|
|
|
|
|
| Stock options |
|
|
|
|
|
| Increase in number of shares authorized for issuance |
1,291,644
|
|
|
|
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