Fair Value of Financial Instruments (Tables)

9 Months Ended

Sep. 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 September 30, 2019 (unaudited)
	Total Fair Value at September 30, 2019		Quoted Prices in Active Markets for Identical Assets (Level 1)		Significant Other Observable Inputs (Level 2)
Assets:
Cash and cash equivalents	$	116,889	$	116,889	$	—
Marketable securities
Corporate debt securities	179,643		247		179,396
Municipal debt securities	165		—		165
Long term marketable securities
Corporate debt securities	585,446		456		584,990
U.S. government agency debt securities	10,996		—		10,996
Other noncurrent assets
Marketable securities - restricted (SERP)	378		1		377
Total assets at fair value	$	893,517	$	117,593	$	775,924

			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 and municipal debt securities	3,148		—		3,148
Other noncurrent assets
Marketable securities - restricted (SERP)	326		1		325
Total assets at fair value	$	775,142	$	192,939	$	582,203

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:

	September 30, 2019			December 31, 2018
	(unaudited)
Corporate and U.S. government agency and municipal debt securities
Amortized cost	$	766,570		$	586,726
Gross unrealized gains	9,756			55
Gross unrealized losses	(76		)	(4,213		)
Total fair value	$	776,250		$	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:

	September 30, 2019
	(unaudited)
Less than 1 year	$	179,808
1 year to 2 years	194,063
2 years to 3 years	201,889
3 years to 4 years	200,490
Greater than 4 years	—
Total	$	776,250

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:

	September 30, 2019				December 31, 2018
	(unaudited)
	Carrying Value		Fair Value (Level 2)		Carrying Value		Fair Value (Level 2)
2023 Notes	$	341,163	$	374,828	$	329,462	$	375,834