Fair Value of Financial Instruments - Cash and Cash Equivalents (Detail) (USD $) In Thousands, unless otherwise specified	Jun. 30, 2013	Mar. 31, 2013	Dec. 31, 2012	Jun. 30, 2012	Mar. 31, 2012	Dec. 31, 2011
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total cash and cash equivalents	$ 1,286,109	$ 1,394,687	$ 1,260,842	$ 1,364,247	$ 1,412,915	$ 1,294,356
Total short term investments	89,902		139
Cost
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total cash and cash equivalents	1,286,109		1,260,842
Total short term investments	89,902		139
Total	1,376,011		1,260,981
Fair Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Total cash and cash equivalents	1,286,184		1,260,844
Total short term investments	89,906		139
Total	1,376,090		1,260,983
Cash and Cash Equivalents | Cost
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and overnight deposits	526,256		458,169
Corporate commercial paper	634,087		642,884
Time deposits	125,766		159,789
Cash and Cash Equivalents | Fair Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Cash and overnight deposits	526,256		458,169
Corporate commercial paper	634,162		642,886
Time deposits	125,766		159,789
Short-term Investments | Cost
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Corporate commercial paper	89,811		0
Time deposits	91		139
Short-term Investments | Fair Value
Fair Value, Balance Sheet Grouping, Financial Statement Captions [Line Items]
Corporate commercial paper	89,815		0
Time deposits	$ 91		$ 139