Summary of Significant Accounting Policies - Additional Information (Detail) (USD $)	9 Months Ended	12 Months Ended
	Sep. 30, 2012	Dec. 31, 2014 Derivative	Dec. 31, 2013 Derivative	Dec. 31, 2012	Jun. 30, 2013
Significant Accounting Policies [Line Items]
Forward contracts outstanding		0	0
Other comprehensive income		$ (31,941,000)	$ (68,170,000)	$ (13,699,000)
Other comprehensive income, foreign currency translation adjustments		32,400,000	64,700,000	11,900,000
Out-of-period adjustment relating to the past period adjustments		3,000,000
Money market fund		30,300,000	33,200,000
Term deposits, maximum maturity period (in months)		3 months
Term deposits		466,600,000	340,300,000
Cash and cash equivalents		143,000,000
Fixed Maturity Plans (FMPs) of mutual funds, at cost		15,886,000	0
Term deposits, noncurrent		110,000	160,000
Depreciation and amortization expense		16,200,000	14,500,000	14,400,000
Favorable adjustment upon review of uncertain tax liabilities	240,000	1,200,000	1,090,000	240,000
Additional tax charge on account of tax dispute		860,000
Tax charges related to deferred tax assets on long-term gain on investment		1,630,000
Valuation allowances		2,616,000
Effective tax rate reconciliation resulting from certain adjustments		21.10%	23.50%	22.80%
Inflation growth rate			4.00%
Additional deferred tax assets and credit to tax expense					550,000
Reversal based on valuation allowance			430,000
Increase from update to apportionment methodology			1,590,000
Decrease in basic and diluted due to revisions in payment of tax			$ 0.04
Impact on earnings per share				$ 0
Foreign exchange gain (loss)		10,700,000	9,000,000	1,300,000
Out-of-period adjustment		3,000,000
Unutilized earned leave expense		5,400,000	5,100,000	4,900,000
Accrual for unutilized earned leave		21,500,000	19,100,000
Restricted Deposits
Significant Accounting Policies [Line Items]
Term deposits, noncurrent		530,000	410,000
Prior Years
Significant Accounting Policies [Line Items]
Increase from update to apportionment methodology			600,000
Bank of America
Significant Accounting Policies [Line Items]
Term deposits		11,440,000
Punjab National Bank
Significant Accounting Policies [Line Items]
Term deposits		10,000,000	29,800,000
Bank Of India
Significant Accounting Policies [Line Items]
Term deposits		3,000,000
Foreign Currency Translation Adjustments
Significant Accounting Policies [Line Items]
Other comprehensive income		(31,994,000)	(71,437,000)	(13,468,000)
Out-of-period adjustment		3,000,000
Minimum
Significant Accounting Policies [Line Items]
Rate of Inflation			4.00%
Maximum
Significant Accounting Policies [Line Items]
Rate of Inflation			11.00%
Minimum Alternate Tax (MAT)
Significant Accounting Policies [Line Items]
Valuation allowances		880,000
Foreign Exchange Forward
Significant Accounting Policies [Line Items]
Foreign exchange forward contracts, notional amount		160,000,000	341,000,000	255,000,000
Derivative contracts expired		160,000,000	341,000,000	315,000,000
Gain on expiration of contracts		4,560,000
Foreign exchange forward contracts outstanding		0	0	0
Loss on expiration of contracts			18,050,000	4,370,000
Foreign Exchange Forward | Minimum
Significant Accounting Policies [Line Items]
Foreign exchange forward contracts, minimum maturity date, months		1 month	1 month	1 month
Foreign Exchange Forward | Maximum
Significant Accounting Policies [Line Items]
Foreign exchange forward contracts, maximum maturity date		6 months	7 months	4 months
Foreign Exchange Forward | Client Contracts
Significant Accounting Policies [Line Items]
Loss on expiration of contracts			11,260,000	2,810,000
Foreign Exchange Forward | Intercompany Contracts
Significant Accounting Policies [Line Items]
Loss on expiration of contracts			$ 6,790,000	$ 1,560,000