| Selected Quarterly Financial Information (Unaudited) [Table Text Block] |
Summarized quarterly financial information for the years ended December 31, 2013 and 2012 is as follows (in thousands): | | | | | | | | | | | | | | | | | | | | Three months ended | | | March 31,
2013 | | June 30,
2013 | | September 30,
2013 | | December 31,
2013 | Revenue | | $ | 61,194 |
| | $ | 57,481 |
| | $ | 58,554 |
| | $ | 60,275 |
| Cost of revenue | | 23,670 |
| | 24,694 |
| | 29,766 |
| | 32,641 |
| Selling, general and administrative expenses | | 14,473 |
| | 15,736 |
| | 15,584 |
| | 16,732 |
| Loss on sale of patent assets | | — |
| | 126 |
| | — |
| | — |
| Operating income | | 23,051 |
| | 16,925 |
| | 13,204 |
| | 10,902 |
| Other income, net | | 51 |
| | 63 |
| | 56 |
| | 43 |
| Income before provision for income taxes | | 23,102 |
| | 16,988 |
| | 13,260 |
| | 10,945 |
| Provision for income taxes | | 8,407 |
| | 6,291 |
| | 4,863 |
| | 3,951 |
| Net income | | $ | 14,695 |
| | $ | 10,697 |
| | $ | 8,397 |
| | $ | 6,994 |
| Net income available to common stockholders: | | | | | | | | | Basic | | $ | 14,678 |
| | $ | 10,691 |
| | $ | 8,395 |
| | $ | 6,994 |
| Diluted | | $ | 14,678 |
| | $ | 10,691 |
| | $ | 8,395 |
| | $ | 6,994 |
| Net income available to common stockholders per common share(1): | | | | | | | | | Basic | | $ | 0.29 |
| | $ | 0.21 |
| | $ | 0.16 |
| | $ | 0.13 |
| Diluted | | $ | 0.28 |
| | $ | 0.20 |
| | $ | 0.16 |
| | $ | 0.13 |
| Other Data: | | | | | | | | | Deferred revenue, including current portion | | $ | 118,177 |
| | $ | 117,573 |
| | $ | 105,230 |
| | $ | 137,743 |
| Stock-based compensation expense | | $ | 3,708 |
| | $ | 4,478 |
| | $ | 3,895 |
| | $ | 4,033 |
|
| | | | | | | | | | | | | | | | | | | | Three months ended | | | March 31,
2012 | | June 30,
2012 | | September 30,
2012 | | December 31,
2012 | Revenue | | $ | 43,849 |
| | $ | 55,238 |
| | $ | 47,044 |
| | $ | 51,557 |
| Cost of revenue | | 18,017 |
| | 20,511 |
| | 21,980 |
| | 21,815 |
| Selling, general and administrative expenses | | 13,223 |
| | 13,533 |
| | 13,147 |
| | 13,687 |
| (Gain) on sale of patent assets | | (177 | ) | | — |
| | — |
| | — |
| Operating income | | 12,786 |
| | 21,194 |
| | 11,917 |
| | 16,055 |
| Other income (expense), net | | (20 | ) | | 47 |
| | 65 |
| | 25 |
| Income before provision for income taxes | | 12,766 |
| | 21,241 |
| | 11,982 |
| | 16,080 |
| Provision for income taxes | | 4,685 |
| | 8,053 |
| | 4,392 |
| | 5,982 |
| Net income | | $ | 8,081 |
| | $ | 13,188 |
| | $ | 7,590 |
| | $ | 10,098 |
| Net income available to common stockholders: | | | | | | | | | Basic | | $ | 7,840 |
| | $ | 12,976 |
| | $ | 7,556 |
| | $ | 10,080 |
| Diluted | | $ | 7,853 |
| | $ | 12,985 |
| | $ | 7,557 |
| | $ | 10,080 |
| Net income available to common stockholders per common share(1): | | | | | | | | | Basic | | $ | 0.16 |
| | $ | 0.26 |
| | $ | 0.15 |
| | $ | 0.20 |
| Diluted | | $ | 0.15 |
| | $ | 0.25 |
| | $ | 0.14 |
| | $ | 0.19 |
| Other Data: | | | | | | | | | Deferred revenue, including current portion | | $ | 105,801 |
| | $ | 105,980 |
| | $ | 98,687 |
| | $ | 104,371 |
| Stock-based compensation expense | | $ | 2,491 |
| | $ | 2,521 |
| | $ | 2,481 |
| | $ | 2,841 |
|
(1) Basic and diluted earnings per share are computed independently for each of the quarters presented. Therefore, the sum of quarterly basic and diluted per share information may not equal annual basic and diluted earnings per share. |