Fair value of financial instruments (Tables)

3 Months Ended

Mar. 31, 2016

Marketable Securities

Schedule of fair value of assets measured on recurring basis

The following fair value hierarchy table presents information about each major category of our financial assets and liabilities measured at fair value on a recurring basis as of March 31, 2016 (in thousands):

	Fair Value Measurement at Reporting Date Using:
	Quoted Prices in		Significant Other		Significant
	Active Markets for		Observable		Unobservable
	Identical Assets		Inputs		Inputs		Balance as of
	(Level 1)		(Level 2)		(Level 3)		March 31, 2016
Cash and cash equivalents	$	657,615	$	—	$	—	$	657,615
Corporate debt securities		—		153,054		—		153,054
Long term investment (Note 7)		32,298		—		—		32,298
Total assets	$	689,913	$	153,054	$	—	$	842,967

The following fair value hierarchy table presents information about each major category of our financial assets measured at fair value on a recurring basis as of December 31, 2015 (in thousands):

	Fair Value Measurement at Reporting Date Using:
	Quoted Prices in		Significant Other		Significant
	Active Markets for		Observable		Unobservable
	Identical Assets		Inputs		Inputs		Balance as of
	(Level 1)		(Level 2)		(Level 3)		December 31, 2015
Cash and cash equivalents	$	521,439	$	—	$	—	$	521,439
Corporate debt securities		—		186,344		—		186,344
Long term investment (Note 7)		35,248		—		—		35,248
Total assets	$	556,687	$	186,344	$	—	$	743,031

Summary of marketable securities portfolio

The following is a summary of our marketable security portfolio as of March 31, 2016 and December 31, 2015, respectively.

			Net		Net
	Amortized		Unrealized		Unrealized		Estimated
	Cost		Gains		Losses		Fair Value
	(in thousands)
March 31, 2016
Corporate debt securities	$	152,657	$	397	$	—	$	153,054
December 31, 2015
Corporate debt securities	$	187,153	$	—	$	(809)	$	186,344