Fair Value of Financial Instruments (Tables)

12 Months Ended

Dec. 31, 2018

Fair Value Disclosures [Abstract]

Schedule of Fair value of Cash and Cash Equivalents by Balance Sheet Grouping

Cash and cash equivalents consist of the following:

	December 31, 2018			December 31, 2017
	Cost		Fair Value	Cost	Fair Value
Cash and cash equivalents:
Cash and overnight deposits	$	427,307	427,307	383,021	383,021
Corporate commercial paper	467,300		467,760	635,345	635,919
Time deposits	29,128		29,128	32,733	32,733
Total cash and cash equivalents	923,735		924,195	1,051,099	1,051,673