Fair Value of Financial Instruments (Tables)

9 Months Ended

Sep. 30, 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:

	September 30, 2018			December 31, 2017
	Cost		Fair Value	Cost	Fair Value
Cash and Cash Equivalents:
Cash and overnight deposits	$	444,650	444,650	383,021	383,021
Corporate commercial paper	520,740		521,292	635,345	635,919
Time deposits	25,222		25,222	32,733	32,733
Total cash and cash equivalents	$	990,612	991,164	1,051,099	1,051,673