Fair Value Measurement (Details) - USD ($)	Mar. 31, 2018	Dec. 31, 2017
Short-term investments:
Transfer of assets from Level 1 to 2	$ 0	$ 0
Transfer of assets from Level 2 to 1	0	0
Transfer of liabilities from Level 1 to 2	0	0
Transfer of liabilities from Level 2 to 1	0	0
Recurring
Short-term investments:
Available-for-sale securities	50,000	50,000
Term deposits	60,000	60,000
Total Assets	110,000	110,000
Level 1 | Recurring
Short-term investments:
Term deposits	60,000	60,000
Total Assets	60,000	60,000
Level 2 | Recurring
Short-term investments:
Available-for-sale securities	50,000	50,000
Total Assets	$ 50,000	$ 50,000