Available for Sale Securities

12 Months Ended

Dec. 31, 2017

Investments Debt And Equity Securities [Abstract]

Available for Sale Securities

4. Available for Sale Securities

Available for sale securities at December 31, 2017 and 2016 consist of the following:

			Gross		Gross
			Unrealized		Unrealized
	Amortized Cost		Gains		Losses			Fair Value
	(in thousands)
December 31, 2017
Cash and cash equivalents	$	70,156	$	—	$	—		$	70,156
Available for sale securities:
Certificates of deposit	$	14,117	—		—			$	14,117
U.S. government debt securities		175,155	—			(352	)		174,803
Corporate debt securities		58,806	—			(90	)		58,716
Total available for sale securities	$	248,078	$	—	$	(442	)	$	247,636
Total cash, cash equivalents, and available for sale securities	$	318,234	$	—	$	(442	)	$	317,792

			Gross		Gross
			Unrealized		Unrealized
	Amortized Cost		Gains		Losses			Fair Value
	(in thousands)
December 31, 2016
Cash and cash equivalents	$	187,335	$	—	$	—		$	187,335
Available for sale securities:
Certificates of deposit	$	12,698	—			—		$	12,698
U.S. government debt securities		50,952	—			(32	)		50,920
Corporate debt securities		9,398	—			(8	)		9,390
Total available for sale securities	$	73,048	$	—	$	(40	)	$	73,008
Total cash, cash equivalents, and available for sale securities	$	260,383	$	—	$	(40	)	$	260,343

The estimated fair value of the Company’s available for sale securities balance at December 31, 2017, by contractual maturity, is as follows:  

Due in one year or less	$	217,884
Due after one year		29,752
Total available for sale securities	$	247,636

There were no realized gains or losses on available for sale securities for the years ended December 31, 2017 or 2016. There were three U.S. government debt securities that had been in an unrealized loss position for more than 12 months as of December 31, 2017 with an aggregate unrealized loss on these securities of $9,000 and fair value of $4.0 million. There were no available for sale securities that had been in an unrealized position for more than 12 months as of December 31, 2016. There were 57 securities in a loss position for less than 12 months at December 31, 2017 with an aggregate unrealized loss on these securities of $433,000 and fair value of $229.5 million. There were 27 securities in a loss position for less than 12 months at December 31, 2016 with an aggregate unrealized loss on these securities of $40,000 and fair value of $60.3 million. The Company considered the decline in the market value of these securities to be primarily attributable to current economic conditions. The contractual terms of these securities do not permit the issuer to settle the securities at a price less than the amortized cost basis of the investment. As it was not more likely than not that the Company would be required to sell these securities before the recovery of their amortized cost basis, which may be at maturity, the Company did not consider these investments to be other-than-temporarily impaired as of December 31, 2017.