Fair Value Measurements (Tables)

12 Months Ended

Dec. 31, 2018

Fair Value Disclosures [Abstract]

Assets And Liabilities Measured At Fair Value On A Recurring Basis

Assets and Liabilities Measured at Fair Value on a Recurring Basis

	As of December 31, 2018		Quoted Prices In Active Markets for Identical Assets (Level 1)		Significant Other Observable Inputs (Level 2)		Significant Unobservable Inputs (Level 3)
	(in thousands)
Assets:
Cash and cash equivalents:
Cash	$	505,363	$	505,363	$	—	$	—
Money market funds	88,126		88,126		—		—
Agency securities	3,296		—		3,296		—
Corporate securities	9,371		—		9,371		—
Government securities	12,610				12,610		—
Available-for-sale securities:
Agency securities	312,948		—		312,948		—
Corporate securities	608,658		—		607,945		713
Municipal securities	2,504		—		2,504		—
Government securities	233,824		—		233,824		—
Prepaid expenses and other current assets:
Foreign currency derivatives	764		—		764		—
Total assets	$	1,777,464	$	593,489	$	1,183,262	$	713
Accrued expenses and other current liabilities:
Foreign currency derivatives	2,543		—		2,543		—
Total liabilities	$	2,543	$	—	$	2,543	$	—

	As of December 31, 2017		Quoted Prices In Active Markets for Identical Assets (Level 1)		Significant Other Observable Inputs (Level 2)		Significant Unobservable Inputs (Level 3)
	(in thousands)
Assets:
Cash and cash equivalents:
Cash	$	556,520	$	556,520	$	—	$	—
Money market funds	555,826		555,826		—		—
Corporate securities	2,784		—		2,784		—
Available-for-sale securities:
Agency securities	439,064		—		439,064		—
Corporate securities	807,692		—		807,299		393
Municipal securities	3,965		—		3,965		—
Government securities	366,123		—		366,123		—
Prepaid expenses and other current assets:
Foreign currency derivatives	2,498		—		2,498		—
Total assets	$	2,734,472	$	1,112,346	$	1,621,733	$	393
Accrued expenses and other current liabilities:
Foreign currency derivatives	814		—		814		—
Total liabilities	$	814	$	—	$	814	$	—

Fair Value, by Balance Sheet Grouping

As of December 31, 2018, the fair value of the 2027 Notes and Convertible Notes, which was determined based on inputs that are observable in the market (Level 2), based on the closing trading price per $100 as of the last day of trading for the year ended December 31, 2018, and carrying value of debt instruments (carrying value excludes the equity component of the Company’s Convertible Notes classified in equity) was as follows (in thousands):

	Fair Value		Carrying Value
2027 Notes	$	717,375	$	741,825
Convertible Senior Notes	$	1,648,567	$	1,155,445