Fair value of financial instruments (Tables)

6 Months Ended

Jun. 30, 2015

Fair value of financial instruments.

Schedule of fair value of assets and liabilities 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 June 30, 2015 (in thousands):

	Fair Value Measurement at Reporting Date Using:
	Quoted Prices in Active Markets for Identical Assets (Level 1)		Significant Other Observable Inputs (Level 2)		Significant Unobservable Inputs (Level 3)		Balance as of June 30, 2015
Cash and cash equivalents	$	439,681	$	—	$	—	$	439,681
Corporate debt securities	—		184,521		—		184,521
Long term investment (Note 7)	67,003		—		—		67,003
Mortgage-backed securities	—		3,267		—		3,267
Total assets	$	506,684	$	187,788	$	—	$	694,472

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, 2014 (in thousands):

	Fair Value Measurement at Reporting Date Using:
	Quoted Prices in Active Markets for Identical Assets (Level 1)		Significant Other Observable Inputs (Level 2)		Significant Unobservable Inputs (Level 3)		Balance as of December 31, 2014
Cash and cash equivalents	$	452,297	$	—	$	—	$	452,297
Corporate debt securities	—		144,402		—		144,402
Mortgage-backed securities	—		3,564		—		3,564
Total assets	$	452,297	$	147,966	$	—	$	600,263

Summary of marketable securities portfolio

	Amortized Cost		Net Unrealized Gains		Net Unrealized Losses			Estimated Fair Value
	(in thousands)
June 30, 2015
Corporate debt securities	$	184,670	$	—	$	(149	)	$	184,521
Mortgage backed securities	1,169		2,098		—			3,267
	$	185,839	$	2,098	$	(149	)	$	187,788
December 31, 2014
Corporate debt securities	$	144,684	$	—	$	(282	)	$	144,402
Mortgage backed securities	1,461		2,103		—			3,564
	$	146,145	$	2,103	$	(282	)	$	147,966