Fair Value of Financial Instruments (Tables)

6 Months Ended

Jun. 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:

	June 30, 2018			December 31, 2017
	Cost		Fair Value	Cost	Fair Value
Cash and Cash Equivalents:
Cash and overnight deposits	$	527,095	527,095	383,021	383,021
Corporate commercial paper	467,528		467,898	635,345	635,919
Time deposits	26,231		26,231	32,733	32,733
Total cash and cash equivalents	$	1,020,854	1,021,224	1,051,099	1,051,673