Short-term and Long-term Investments (Tables)

12 Months Ended

Dec. 31, 2017

Investments, Debt and Equity Securities [Abstract]

Summary of Amortized Cost, Gross Unrealized Gains and Losses and Fair Value of Investments

The following table summarizes the amortized cost, gross unrealized gains and losses and fair value of available-for-sale investments as of December 31, 2017:



	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Aggregate Fair Value
U.S. government debt securities	$	6,000	$	—	$	(2	)	$	5,998
Certificates of deposit	275		—		—			275
Total	$	6,275	$	—	$	(2	)	$	6,273

The following table summarizes the amortized cost, gross unrealized gains and losses and fair value of available-for-sale investments as of December 31, 2016:



	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Aggregate Fair Value
U.S. government debt securities	$	180,412	$	5	$	(94	)	$	180,323
Certificates of deposit	272		—		—			272
Total	$	180,684	$	5	$	(94	)	$	180,595

- Definition

Tabular disclosure of available-for-sale securities which includes, but is not limited to, changes in the cost basis and fair value, fair value and gross unrealized gain (loss), fair values by type of security, contractual maturity and classification, amortized cost basis, contracts to acquire securities to be accounted for as available-for-sale, debt maturities, transfers to trading, change in net unrealized holding gain (loss) net of tax, continuous unrealized loss position fair value, aggregate losses qualitative disclosures, other than temporary impairment (OTTI) losses or other disclosures related to available for sale securities.

+ References + Details