Fair Value Measurements - Schedule of Assets Measured or Disclosed at Fair Value on Recurring Basis (Detail) - USD ($)
$ in Thousands |
Dec. 31, 2015 |
Dec. 31, 2014 |
| Held-to-maturity investments |
|
|
| U.S. treasury securities and government agency bonds |
$ 38,504
|
$ 72,532
|
| Assets held in restriction |
|
|
| Total |
85,177
|
94,337
|
| Money Market Fund [Member] |
|
|
| Cash equivalents |
|
|
| Money market fund |
45,557
|
20,425
|
| Assets held in restriction |
|
|
| Restricted investments, at fair value |
1,116
|
|
| Money Market Fund And Certificate Of Deposit [Member] |
|
|
| Assets held in restriction |
|
|
| Restricted investments, at fair value |
|
1,380
|
| US Treasury Securities [Member] |
|
|
| Held-to-maturity investments |
|
|
| U.S. treasury securities and government agency bonds |
38,504
|
|
| U.S. Government Treasury and Agency Securities [Member] |
|
|
| Held-to-maturity investments |
|
|
| U.S. treasury securities and government agency bonds |
|
72,532
|
| Level 1[Member] |
|
|
| Assets held in restriction |
|
|
| Total |
45,557
|
20,425
|
| Level 1[Member] | Money Market Fund [Member] |
|
|
| Cash equivalents |
|
|
| Money market fund |
45,557
|
20,425
|
| Level 2 [Member] |
|
|
| Assets held in restriction |
|
|
| Total |
39,620
|
73,912
|
| Level 2 [Member] | Money Market Fund [Member] |
|
|
| Assets held in restriction |
|
|
| Restricted investments, at fair value |
1,116
|
|
| Level 2 [Member] | Money Market Fund And Certificate Of Deposit [Member] |
|
|
| Assets held in restriction |
|
|
| Restricted investments, at fair value |
|
1,380
|
| Level 2 [Member] | US Treasury Securities [Member] |
|
|
| Held-to-maturity investments |
|
|
| U.S. treasury securities and government agency bonds |
$ 38,504
|
|
| Level 2 [Member] | U.S. Government Treasury and Agency Securities [Member] |
|
|
| Held-to-maturity investments |
|
|
| U.S. treasury securities and government agency bonds |
|
$ 72,532
|