Income Taxes - Additional Information (Detail) (USD $) In Millions, unless otherwise specified	1 Months Ended	3 Months Ended					9 Months Ended	12 Months Ended												1 Months Ended		12 Months Ended								1 Months Ended	12 Months Ended
	Jul. 13, 2011	Sep. 30, 2012	Sep. 30, 2011	Jun. 30, 2011	Mar. 31, 2011	Sep. 30, 2010	Sep. 30, 2011	Dec. 31, 2012	Dec. 31, 2011	Dec. 31, 2010	Dec. 31, 2005	Dec. 31, 2004	Dec. 31, 2003	Dec. 31, 2002	Dec. 31, 2009 Software Development Entity	Apr. 30, 2008 Tax Exemption Period Entity	Dec. 31, 2012 Mumbai Tax Exemption Period Entity	Dec. 31, 2012 Mumbai Completion of Tax Holiday Period Entity	Dec. 31, 2012 Minimum Alternate Tax (MAT)	Feb. 28, 2013 Subsequent Event	Feb. 11, 2013 Subsequent Event	Dec. 31, 2011 Prior Years	Dec. 31, 2010 Carry Back Of Losses	Dec. 31, 2012 Certain Units In Sez First Five Years	Dec. 31, 2012 Certain Units In Sez Additional Two Years	Dec. 31, 2012 Certain Units In Sez Additional Three Years	Dec. 31, 2012 New Units In Sez First Five Years	Dec. 31, 2012 New Units In Sez Next Five Years	Dec. 31, 2012 New Units In Sez Another Five Years	Apr. 30, 2008 Three Units In Mumbai First Five Years	Dec. 31, 2012 Three Units In Mumbai First Five Years	Mar. 31, 2012 Three Units In Mumbai First Five Years	Mar. 31, 2012 Unit in Chennai First Five Years	Dec. 31, 2012 Other Disputes
Income Taxes [Line Items]
Corporate income taxes, exemption percentage																								100.00%	50.00%	50.00%	100.00%	50.00%	50.00%	50.00%	100.00%	100.00%	100.00%
Number of units															1	4	6	1
Exemption from corporate income taxes								10 years
Corporate income taxes, years								15 years
Benefit of tax Holiday under Indian Income Tax								$ 24.6	$ 19.1	$ 25.0
Accrued taxes, likely amount								183.9
Statutory rate								35.00%	35.00%	35.00%
Effective income tax rate								22.70%	20.40%	15.00%
Reversal of provision of uncertain tax liability								0.24
Income taxes paid against liabilities for unrecognized tax benefits								20.58	18.24
Unrecognized tax liability								24.94	18.41	19.71
Expense recognized for accrued interest and penalties								1.46	0
Interest previously accrued, reversal										0.33
Accrued interest and penalties related to unrecognized tax benefits								1.40	0.06
Unrecognized tax benefits, tax disputes								1.6
Unrecognized tax benefits, potential tax disputes								3.2
Favorable adjustment upon review of uncertain tax liabilities				0.90	3.20			0.24	3.50	1.28
Reversal of tax reserve due to reversal of previous position			0.30	0	0.30		2.60	0.24	3.46
Unrecognized Tax Benefits, Decreases Resulting From Reversal Of Valuation Allowance			0.6				0.6
Reversal from reconciliation of tax returns to book provision			1.2						1.2	0.5
Unrecognized Tax Benefits Increases Resulting From Update To Apportionment Methodology									1.3													0.8
Effective tax rate reconciliation resulting from certain adjustments								22.80%	23.00%	16.60%
Deferred tax asset, change in amount										0.2													0.2
Unrecognized Indian income tax liabilities													4.94	4.94																				1.65
Income tax liability recognized											0.80	0.80																						0.85
Income tax adjustments provision reversal										0.33
Income tax audit, service tax objection amount		0.50				3.85		5.30
Service tax audit objection received	3.0
Closure of service tax audit objection amount								0.85
Service tax return with show cause notice								2.23
Service tax penalty and interest demanded by tax department																					4.3
Interest percentage on service tax penalty																				18.00%
Local tax liability gross								4.3
Local tax liability net								2.7
Minimum alternate tax credit expiration period																			10 years
Minimum Alternate Tax Credit																			$ 16.82