Cash and Cash Equivalents and Short Term Investments - Additional Information (Detail) - USD ($)	9 Months Ended
	Sep. 30, 2015	Dec. 31, 2014
Restricted Cash and Cash Equivalents Items [Line Items]
Cash and cash equivalent and short term investments	$ 980,500,000
Money market fund	0	$ 30,300,000
Term deposits	$ 409,100,000	466,600,000
Term deposits, maximum maturity period (in months)	3 months
Cash and cash equivalents	$ 368,900,000
Fixed Maturity Plans (FMPs) of mutual funds, at cost	0	15,886,000
Non current term deposits with banks	80,000	110,000
Bank of America
Restricted Cash and Cash Equivalents Items [Line Items]
Term deposits	30,200,000
Punjab National Bank and Bank of India
Restricted Cash and Cash Equivalents Items [Line Items]
Term deposits	108,000,000	13,000,000
Restricted Deposits
Restricted Cash and Cash Equivalents Items [Line Items]
Term deposits	1,250,000	$ 530,000
Indian Subsidiaries
Restricted Cash and Cash Equivalents Items [Line Items]
Cash and cash equivalent and short term investments	923,700,000
Indian Subsidiaries | Us Dollar Denominated
Restricted Cash and Cash Equivalents Items [Line Items]
Cash and cash equivalent and short term investments	542,000,000
Indian Subsidiaries | Indian Rupee
Restricted Cash and Cash Equivalents Items [Line Items]
Cash and cash equivalent and short term investments	$ 381,700,000