Short-term Investments - Assets Classified on Consolidated Balance Sheets (Details) - USD ($) $ in Thousands		Jun. 30, 2015	Dec. 31, 2014
Schedule of Available-for-sale Securities [Line Items]
Total		$ 2,801,692	$ 1,614,190
Fair Value, Measurements, Recurring [Member]
Schedule of Available-for-sale Securities [Line Items]
Total		2,801,692	1,614,190
Cash and cash equivalents [Member] | Fair Value, Measurements, Recurring [Member]
Schedule of Available-for-sale Securities [Line Items]
Total		2,293,872	1,113,608
Short-term investments [Member] | Fair Value, Measurements, Recurring [Member]
Schedule of Available-for-sale Securities [Line Items]
Total		502,886	494,888
Other non-current assets [Member] | Fair Value, Measurements, Recurring [Member]
Schedule of Available-for-sale Securities [Line Items]
Total	[1]	$ 4,934	$ 5,694

[1] Primarily restricted cash that is related to workers compensation deposits.