Fair Value of Financial Instruments (Tables)

3 Months Ended

Mar. 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:

	March 31, 2018			December 31, 2017
	Cost		Fair Value	Cost	Fair Value
Cash and Cash Equivalents:
Cash and overnight deposits	$	452,028	452,028	383,021	383,021
Corporate commercial paper	643,085		644,225	635,345	635,919
Time deposits	37,788		37,788	32,733	32,733
Total cash and cash equivalents	$	1,132,901	1,134,041	1,051,099	1,051,673