3.	Investments

As of June 30, 2017, we primarily invested our excess cash in debt instruments of the U.S. Treasury, financial institutions, corporations, and U.S. government agencies with strong credit ratings and an investment grade rating at or above A-1, P-1 or F-1 by Moody’s, Standard & Poor’s or Fitch, respectively. We have established guidelines relative to diversification and maturities that maintain safety and liquidity. We periodically review and modify these guidelines to maximize trends in yields and interest rates without compromising safety and liquidity.

As of June 30, 2017, all of the securities held by us had a contractual maturity of one year or less and all of our available-for-sale securities were available to us for use in our current operations and are classified as current assets.

As of December 31, 2016, we only invested in money market funds.

The following is a summary of our investments at June 30, 2017 (in thousands):

				Gross Unrealized
	Cost			Gains			Losses				Estimated Fair Value
Available-for-sale securities (1):
Corporate debt securities		$	40,250		$	—		$	(25	)		$	40,225
Other municipal debt securities			3,000			—			(2	)			2,998
Total available-for-sale securities		$	43,250		$	—		$	(27	)		$	43,223

(1)	Our available-for-sale securities are held at amortized cost.

Investments we consider to be temporarily impaired at June 30, 2017 were as follows (in thousands):

			Less than 12 Months of Temporary Impairment							More than 12 Months of Temporary Impairment						Total Temporary Impairment
	Number of Investments		Estimated Fair Value			Unrealized Losses				Estimated Fair Value			Unrealized Losses			Estimated Fair Value			Unrealized Losses
Corporate debt securities		17		$	31,437		$	(25	)		$	—		$	—		$	31,437		$	(25	)
Other municipal debt securities		1			2,998			(2	)			—			—			2,998			(2	)
Total temporarily impaired securities		18		$	34,435		$	(27	)		$	—		$	—		$	34,435		$	(27	)

We believe that the decline in value of these securities is temporary and are primarily related to the change in market interest rates since purchase. We believe it is more likely than not that we will be able to hold our debt securities to maturity. Therefore, we anticipate a full recovery of our debt securities’ amortized cost basis at maturity.