Fair Value of Financial Instruments (Tables)

12 Months Ended

Dec. 31, 2019

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 as of 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 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

			Fair Value Measurements as of December 31, 2018
	Total Fair Value at December 31, 2018		Quoted Prices in Active Markets for Identical Assets (Level 1)		Significant Other Observable Inputs (Level 2)
Assets:
Cash and cash equivalents
Cash	$	106,918	$	106,918	$	—
Money market funds	85,330		85,330		—
Marketable securities
Corporate debt securities	163,770		245		163,525
Long term marketable securities
Corporate debt securities	415,650		445		415,205
U.S. government agency debt securities	2,983		—		2,983
Municipal debt securities	165		—		165
Other noncurrent assets
Marketable securities - restricted (SERP)	326		1		325
Total assets at fair value	$	775,142	$	192,939	$	582,203

Schedule of unrestricted marketable securities

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

	December 31, 2019			December 31, 2018
Corporate and U.S. government agency and municipal debt securities
Amortized cost	$	747,598		$	586,726
Gross unrealized gains	10,031			55
Gross unrealized losses	(164		)	(4,213		)
Total fair value	$	757,465		$	582,568

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):

	December 31, 2019
Less Than 1 Year	$	165,692
1 year to 2 years	188,378
2 year to 3 years	201,491
3 years to 4 years	201,904
Greater Than 4 Years	—
Total	$	757,465

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):

	December 31, 2019				December 31, 2018
	Carrying Value		Fair Value (Level 2)		Carrying Value		Fair Value (Level 2)
2023 Notes	$	345,170	$	366,023	$	329,462	$	375,834