Accounts Payable and Accrued Expenses (Details) (USD $) In Thousands, unless otherwise specified	Mar. 31, 2015	Dec. 31, 2014
Components of accounts payable and accrued expenses
Accounts payable	$ 35,062us-gaap_AccountsPayableCurrent	$ 32,701us-gaap_AccountsPayableCurrent
Accrued payroll and related expenses	43,445us-gaap_AccruedSalariesCurrent	39,845us-gaap_AccruedSalariesCurrent
Accrued subcontractor fees	5,092hil_AccruedSubcontractorFees	3,930hil_AccruedSubcontractorFees
Accrued agency fees	5,598hil_AccruedAgencyFees	6,920hil_AccruedAgencyFees
Accrued legal and professional fees	1,037us-gaap_AccruedProfessionalFeesCurrent	968us-gaap_AccruedProfessionalFeesCurrent
Other accrued expenses	7,284us-gaap_OtherAccruedLiabilitiesCurrent	7,704us-gaap_OtherAccruedLiabilitiesCurrent
Accounts payable and accrued expenses, net	$ 97,518	$ 92,068

Carrying value as of the balance sheet date of obligations incurred through that date and payable for professional fees, such as for legal and accounting services received. Used to reflect the current portion of the liabilities (due within one year or within the normal operating cycle if longer).

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Carrying value as of the balance sheet date of the obligations incurred through that date and payable for employees' services provided. Used to reflect the current portion of the liabilities (due within one year or within the normal operating cycle if longer).

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- Definition

Carrying value as of the balance sheet date of obligations incurred through that date and payable arising from transactions not otherwise specified in the taxonomy. Used to reflect the current portion of the liabilities (due within one year or within the normal operating cycle if longer).

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