Marketable Securities (Details) - USD ($)
$ in Thousands |
Dec. 31, 2015 |
Dec. 31, 2014 |
| Schedule of Available-for-sale Securities [Line Items] |
|
|
| Amortized Cost |
$ 118,725
|
$ 184,796
|
| Unrealized Gains |
0
|
5
|
| Unrealized Losses |
(79)
|
(44)
|
| Fair Value |
118,646
|
184,757
|
| Included in cash and cash equivalents [Member] |
|
|
| Schedule of Available-for-sale Securities [Line Items] |
|
|
| Amortized Cost |
4,038
|
3,480
|
| Unrealized Gains |
0
|
0
|
| Unrealized Losses |
(1)
|
0
|
| Fair Value |
4,037
|
3,480
|
| Included in marketable securities [Member] |
|
|
| Schedule of Available-for-sale Securities [Line Items] |
|
|
| Amortized Cost |
101,334
|
175,093
|
| Unrealized Gains |
0
|
5
|
| Unrealized Losses |
(60)
|
(41)
|
| Fair Value |
101,274
|
175,057
|
| Included in marketable securities, noncurrent [Member] |
|
|
| Schedule of Available-for-sale Securities [Line Items] |
|
|
| Amortized Cost |
13,353
|
6,223
|
| Unrealized Gains |
0
|
0
|
| Unrealized Losses |
(18)
|
(3)
|
| Fair Value |
13,335
|
6,220
|
| U.S. agency obligations [Member] |
|
|
| Schedule of Available-for-sale Securities [Line Items] |
|
|
| Amortized Cost |
83,763
|
177,297
|
| Unrealized Gains |
0
|
4
|
| Unrealized Losses |
(48)
|
(44)
|
| Fair Value |
83,715
|
177,257
|
| U.S. treasury securities [Member] |
|
|
| Schedule of Available-for-sale Securities [Line Items] |
|
|
| Amortized Cost |
33,924
|
5,580
|
| Unrealized Gains |
0
|
1
|
| Unrealized Losses |
(31)
|
0
|
| Fair Value |
33,893
|
5,581
|
| Money market mutual funds [Member] |
|
|
| Schedule of Available-for-sale Securities [Line Items] |
|
|
| Amortized Cost |
1,038
|
1,919
|
| Unrealized Gains |
0
|
0
|
| Unrealized Losses |
0
|
0
|
| Fair Value |
$ 1,038
|
$ 1,919
|