Fair value of financial instruments (Tables)

3 Months Ended

Mar. 31, 2013

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 March 31, 2013 (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 March 31, 2013
Cash and cash equivalents	$	265,814	$	—	$	—	$	265,814
Mortgage-backed securities	—		4,365		—		4,365
Total assets	$	265,814	$	4,365	$	—	$	270,179

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 December 31, 2012 (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, 2012
Cash and cash equivalents	$	224,057	$	—	$	—	$	224,057
Mortgage-backed securities	—		4,361		—		4,361
Total assets	$	224,057	$	4,361	$	—	$	228,418

Summary of marketable security portfolio

	Amortized Cost		Net Unrealized Gains		Net Unrealized Losses		Estimated Fair Value
	(in thousands)
March 31, 2013
Mortgage backed securities	$	2,366	$	1,999	$	—	$	4,365
	$	2,366	$	1,999	$	—	$	4,365
December 31, 2012
Mortgage backed securities	$	2,483	$	1,878	$	—	$	4,361
	$	2,483	$	1,878	$	—	$	4,361