Fair Value of Financial Instruments (Tables)

3 Months Ended

Mar. 31, 2015

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:

	March 31, 2015			December 31, 2014
	Cost		Fair Value	Cost	Fair Value
Cash and Cash Equivalents:
Cash and overnight deposits	$	548,705	548,705	531,312	531,312
Corporate commercial paper	441,254		441,332	356,468	356,536
Time deposits	43,185		43,185	39,327	39,327
Total cash and cash equivalents	1,033,144		1,033,222	927,107	927,175
Short-Term Investments:
Corporate commercial paper	—		—	40,295	40,350
Time deposits	61		61	41	41
Total short-term investments	61		61	40,336	40,391
Total	$	1,033,205	1,033,283	967,443	967,566