Fair Value of Financial Instruments (Tables)

6 Months Ended

Jun. 30, 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, in thousands of dollars:

			Fair Value Measurements at June 30, 2019 (unaudited)
	Total Fair Value at June 30, 2019		Quoted Prices in Active Markets for Identical Assets (Level 1)		Significant Other Observable Inputs (Level 2)
Assets:
Cash and cash equivalents	$	87,344	$	87,344	$	—
Marketable securities
Corporate debt securities	171,222		247		170,975
Long term marketable securities
Corporate debt securities	558,755		454		558,301
U.S. government agency debt securities	34,999		—		34,999
Other non-current assets
Marketable securities - restricted (SERP)	387		1		386
Total assets at fair value	$	852,707	$	88,046	$	764,661

			Fair Value Measurements at 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	$	192,248	$	192,248	$	—
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	3,148		—		3,148
Other non-current assets
Marketable securities - restricted (SERP)	326		1		325
Total assets at fair value	$	775,142	$	192,939	$	582,203

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, in thousands of dollars:

	June 30, 2019				December 31, 2018
	(unaudited)
	Carrying Value		Fair Value (Level 2)		Carrying Value		Fair Value (Level 2)
2023 Notes	$	337,210	$	392,689	$	329,462	$	375,834

Schedule of unrestricted available-for-sale marketable securities

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

	June 30, 2019			December 31, 2018
	(unaudited)
Corporate and U.S. government agency debt securities
Amortized cost	$	757,206		$	586,726
Gross unrealized gains	7,966			55
Gross unrealized losses	(196		)	(4,213		)
Total fair value	$	764,976		$	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, in thousands of dollars:

	June 30, 2019
	(unaudited)
Less than 1 year	$	171,222
1 year to 2 years	192,488
2 years to 3 years	200,597
3 years to 4 years	200,669
Greater than 4 years	—
Total	$	764,976