Fair Value of Financial Instruments (Tables)

12 Months Ended

Dec. 31, 2014

Fair Value Disclosures [Abstract]

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

Cash, cash equivalents and short-term investments consist of the following:

	December 31, 2014			December 31, 2013
	Cost		Fair Value	Cost	Fair Value
Cash and cash equivalents:
Cash and overnight deposits	$	531,312	531,312	590,317	590,317
Corporate commercial paper	356,468		356,536	629,923	629,990
Time deposits	39,327		39,327	27,412	27,412
Total cash and cash equivalents	927,107		927,175	1,247,652	1,247,719
Short-term investments:
Corporate commercial paper	40,295		40,350	26,296	26,321
Time deposits	41		41	41	41
Total short-term investments	40,336		40,391	26,337	26,362
Total	$	967,443	967,566	1,273,989	1,274,081