Income Taxes - Additional Information (Detail)		3 Months Ended											9 Months Ended			12 Months Ended
	Jul. 13, 2011 USD ($)	Sep. 30, 2015 USD ($)	Jun. 30, 2015 USD ($)	Mar. 31, 2015 USD ($) Entity	Sep. 30, 2014	Jun. 30, 2014 USD ($)	Dec. 31, 2013 USD ($)	Mar. 31, 2013 Entity	Sep. 30, 2012 USD ($)	Mar. 31, 2012 USD ($) Entity	Dec. 31, 2011 USD ($)	Sep. 30, 2010 USD ($)	Sep. 30, 2015 USD ($)	Sep. 30, 2014	Sep. 30, 2012 USD ($)	Mar. 31, 2012 Entity	Dec. 31, 2010 USD ($)	Dec. 31, 2014 USD ($)	Dec. 31, 2007 USD ($)	Dec. 31, 2005 USD ($)
Income Taxes [Line Items]
Statutory provision		35.00%			35.00%								35.00%	35.00%
Effective holiday tax rate		50.00%
Reversed provision for tax				$ 230,000
Provision for tax to a separate particular tax provision				70,000
Valuation allowance		$ 0		$ 790,000									$ 0
Expense recognized for accrued interest and penalties		40,000
Accrued interest and penalties related to unrecognized tax benefits		1,280,000											1,280,000					$ 1,320,000
Income taxes paid against liabilities for unrecognized tax benefits		40,480,000											40,480,000					35,860,000
Unrecognized tax liability		48,540,000											48,540,000					40,470,000
Unrecognized tax benefits, tax disputes													1,510,000
Unrecognized tax benefits, potential tax disputes													$ 3,070,000
Exemption from corporate income taxes													10 years
Corporate income taxes, years													15 years
Income tax adjustments provision reversal																	$ 330,000
Provision for unrecognized tax benefit against tax dispute		110,000											$ 110,000					860,000
Favorable adjustment upon review of tax liabilities															$ 240,000
Branch Profit Tax (BPT)													15.00%
Accumulated deferred tax liability on BPT																			$ 1,730,000
Additional branch profit taxes if profits were not permanently invested		7,260,000											$ 7,260,000
Accrued taxes, likely amount		299,500,000											299,500,000
Income tax audit, service tax objection amount							$ 710,000		$ 450,000			$ 3,850,000
Service tax audit objection received	$ 3,000,000
Closure of service tax audit objection amount		850,000											850,000
Service tax return with show cause notice													2,040,000
Service tax including penalty and interest demanded by tax department		$ 3,950,000											$ 3,950,000
Interest percentage on service tax penalty													18.00%
Local tax expense													$ 3,400,000
Local tax liability gross																		5,900,000
Local tax liability net																		$ 3,800,000
Two Thousand Two To Two Thousand Five Financial Years
Income Taxes [Line Items]
Unrecognized Indian income tax liabilities																				$ 4,780,000
Income tax liability recognized																				$ 720,000
Fourth Quarter Twenty Eleven
Income Taxes [Line Items]
Income tax audit, service tax objection amount						$ 580,000
Received service tax refund						320,000					$ 150,000
First Quarter Twenty Twelve
Income Taxes [Line Items]
Received service tax refund										$ 130,000
Fourth Quarter Twenty Thirteen
Income Taxes [Line Items]
Income tax audit, service tax objection amount						50,000
Received service tax refund						200,000
July 2013 - March 2014
Income Taxes [Line Items]
Income tax audit, service tax objection amount			$ 300,000
Received service tax refund			$ 512,000
Second Quarter Two Thousand Fourteen
Income Taxes [Line Items]
Income tax audit, service tax objection amount						120,000
Received service tax refund						$ 120,000
Mumbai
Income Taxes [Line Items]
Number of units | Entity								3		1						1
Five Years
Income Taxes [Line Items]
Effective holiday tax rate													100.00%
India Tax Authority | Finance Act 2015
Income Taxes [Line Items]
Cess on services													2.00%
Minimum
Income Taxes [Line Items]
Increase in Minimum Alternative Tax rate													20.96%
Minimum | India Tax Authority
Income Taxes [Line Items]
Increase in surcharge rate		10.00%											10.00%
Increase in corporate tax rate													33.99%
Increase in dividend distribution tax													16.99%
Increase in service tax rate													12.36%
Maximum | Finance Act 2015
Income Taxes [Line Items]
Increase in Minimum Alternative Tax rate													21.34%
Maximum | India Tax Authority | Finance Act 2015
Income Taxes [Line Items]
Increase in surcharge rate		12.00%											12.00%
Increase in corporate tax rate													34.60%
Increase in dividend distribution tax													17.30%
Increase in service tax rate													14.00%
Unit in Chennai
Income Taxes [Line Items]
Number of units | Entity				1						1						1
Unit in Chennai | First Five Years
Income Taxes [Line Items]
Corporate income taxes, exemption percentage				100.00%												100.00%
Unit In Pune | KPO SEZ
Income Taxes [Line Items]
Number of units | Entity								1
Unit In Pune | IT SEZ
Income Taxes [Line Items]
Number of units | Entity								2
Unit In Pune | First Five Years
Income Taxes [Line Items]
Corporate income taxes, exemption percentage								100.00%
Other Disputes
Income Taxes [Line Items]
Unrecognized Indian income tax liabilities		$ 1,580,000											$ 1,580,000
Income tax liability recognized		790,000											$ 790,000
Certain Units In Sez | First Five Years
Income Taxes [Line Items]
Corporate income taxes, exemption percentage													100.00%
Certain Units In Sez | Additional Two Years
Income Taxes [Line Items]
Corporate income taxes, exemption percentage													50.00%
Certain Units In Sez | Additional Three Years
Income Taxes [Line Items]
Corporate income taxes, exemption percentage													50.00%
New Units In Sez | First Five Years
Income Taxes [Line Items]
Corporate income taxes, exemption percentage													100.00%
New Units In Sez | Next Five Years
Income Taxes [Line Items]
Corporate income taxes, exemption percentage													50.00%
New Units In Sez | Another Five Years
Income Taxes [Line Items]
Corporate income taxes, exemption percentage													50.00%
Minimum Alternate Tax (MAT)
Income Taxes [Line Items]
Valuation allowance		1,590,000											$ 1,590,000
Minimum alternate tax credit expiration period													10 years
Valuation allowance, net tax charge		$ 27,160,000											$ 27,160,000