Fair Value of Financial Instruments (Tables)

6 Months Ended

Jun. 30, 2020

Fair Value Disclosures [Abstract]

Schedule of fair value of the financial assets and liabilities

The Company’s financial assets that are required to be measured at fair value on a recurring basis are as follows (dollars in thousands):

			Fair Value Measurements at June 30, 2020 (unaudited)
	Total Fair Value at June 30, 2020		Quoted Prices in Active Markets for Identical Assets (Level 1)		Significant Other Observable Inputs (Level 2)
Assets:
Cash and cash equivalents
Cash	$	183,703	$	183,703	$	—
Money market funds	27,272		27,272		—
Marketable securities
Corporate debt securities	163,839		—		163,839
Municipal debt securities	—		—		—
Long term marketable securities
Corporate debt securities	353,659		259		353,400
U.S. government agency debt securities	5,014		—		5,014
Other noncurrent assets
Marketable securities - restricted (SERP)	431		1		430
Total assets at fair value	$	733,918	$	211,235	$	522,683

			Fair Value Measurements at December 31, 2019
	Total Fair Value at December 31, 2019		Quoted Prices in Active Markets for Identical Assets (Level 1)		Significant Other Observable Inputs (Level 2)
Assets:
Cash and cash equivalents
Cash	$	78,912	$	78,912	$	—
Money market funds	102,469		102,469		—
Marketable securities
Corporate debt securities	165,527		—		165,527
Municipal debt securities	165		—		165
Long term marketable securities
Corporate debt securities	571,828		254		571,574
U.S. government agency and municipal debt securities	19,945		—		19,945
Other noncurrent assets
Marketable securities - restricted (SERP)	418		3		415
Total assets at fair value	$	939,264	$	181,638	$	757,626

Schedule of unrestricted available-for-sale marketable securities

Unrestricted available-for-sale marketable securities held by the Company are as follows, (dollars in thousands):

	June 30, 2020		December 31, 2019
	(unaudited)
Corporate and U.S. government agency and municipal debt securities
Amortized cost	$	507,375	$	747,598
Gross unrealized gains	15,525		10,031
Gross unrealized losses	(388)		(164)
Total fair value	$	522,512	$	757,465

Schedule of contractual maturities of the unrestricted available-for-sale marketable securities held

The contractual maturities of the unrestricted available-for-sale marketable securities held by the Company are as follows, (dollars in thousands):

	June 30, 2020
	(unaudited)
Less than 1 year	$	163,839
1 year to 2 years	143,987
2 years to 3 years	149,688
3 years to 4 years	64,998
Greater than 4 years	—
Total	$	522,512

Schedule of financial liabilities that are not carried at fair value

The following table sets forth the Company’s financial liabilities that are not carried at fair value, (dollars in thousands):

	June 30, 2020				December 31, 2019
	(unaudited)
	Carrying Value		Fair Value (Level 2)		Carrying Value		Fair Value (Level 2)
Convertible notes, net	$	353,349	$	356,213	$	345,170	$	366,023