Available-for-Sale Securities and Fair Value Measurements

Our available-for-sale securities included:



	Fair Value Hierarchy Level	Estimated Fair Value
	Fair Value Hierarchy Level	March 31, 2019		December 31, 2018
		(in thousands)
Corporate bonds	Level 2	$	70,545	$	54,469
Commercial paper	Level 2	35,738		67,906
Asset-backed securities	Level 2	28,951		10,965
Repurchase agreements	Level 2	15,000		15,000
U.S. treasury securities	Level 1	30,863		39,287
Money market funds	Level 1	12,364		4,583
Total Marketable securities		$	193,461	$	192,210

Classified as:
Cash equivalents		$	27,364	$	27,075
Short-term marketable securities		137,255		165,135
Long-term marketable securities		28,842		—
Total marketable securities		$	193,461	$	192,210

We estimate the fair value of marketable securities classified as Level 1 using quoted market prices for these or similar investments obtained from a commercial pricing service. We estimate the fair value of marketable securities classified as Level 2 using inputs that may include benchmark yields, reported trades, broker/dealer quotes and issuer spreads.

As of March 31, 2019, all our marketable securities had original maturities of less than two years. The weighted-average maturity of our holdings was six months. As of March 31, 2019, of our long-term marketable securities have a remaining maturity of 12 to 18 months. None of our marketable securities changed from one fair value hierarchy to another during the three months ended March 31, 2019.