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Stockholders' Equity, Equity Incentive Plans and Warrants (Schedule of Fair Value Assumptions) (Details)
12 Months Ended
Dec. 31, 2014
Dec. 31, 2013
Dec. 31, 2012
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Forfeiture Rate, Minimum 0.00%hill_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedForfeitureRateMinimum 0.00%hill_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedForfeitureRateMinimum 0.00%hill_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedForfeitureRateMinimum
Forfeiture Rate, Maximum 10.05%hill_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedForfeitureRateMaximum 9.45%hill_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedForfeitureRateMaximum 10.62%hill_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedForfeitureRateMaximum
EIP and NEDSOP [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Risk-free interest rate 1.59%us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRate
/ us-gaap_PlanNameAxis
= hill_EipAndNedsopMember
1.07%us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRate
/ us-gaap_PlanNameAxis
= hill_EipAndNedsopMember
1.19%us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRate
/ us-gaap_PlanNameAxis
= hill_EipAndNedsopMember
Expected dividend yield 0.00%us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedDividendRate
/ us-gaap_PlanNameAxis
= hill_EipAndNedsopMember
0.00%us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedDividendRate
/ us-gaap_PlanNameAxis
= hill_EipAndNedsopMember
0.00%us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedDividendRate
/ us-gaap_PlanNameAxis
= hill_EipAndNedsopMember
Volatility 70.00%us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRate
/ us-gaap_PlanNameAxis
= hill_EipAndNedsopMember
82.00%us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRate
/ us-gaap_PlanNameAxis
= hill_EipAndNedsopMember
81.00%us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRate
/ us-gaap_PlanNameAxis
= hill_EipAndNedsopMember
Expected Term 4 years 11 months 12 days 5 years 3 months 18 days 5 years 2 months 10 days
2000ESPP [Member]      
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]      
Risk-free interest rate 0.05%us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRate
/ us-gaap_PlanNameAxis
= hill_A2000EsppMember
0.09%us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRate
/ us-gaap_PlanNameAxis
= hill_A2000EsppMember
0.12%us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsRiskFreeInterestRate
/ us-gaap_PlanNameAxis
= hill_A2000EsppMember
Expected dividend yield 0.00%us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedDividendRate
/ us-gaap_PlanNameAxis
= hill_A2000EsppMember
0.00%us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedDividendRate
/ us-gaap_PlanNameAxis
= hill_A2000EsppMember
0.00%us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedDividendRate
/ us-gaap_PlanNameAxis
= hill_A2000EsppMember
Volatility 60.00%us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRate
/ us-gaap_PlanNameAxis
= hill_A2000EsppMember
63.00%us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRate
/ us-gaap_PlanNameAxis
= hill_A2000EsppMember
64.00%us-gaap_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsExpectedVolatilityRate
/ us-gaap_PlanNameAxis
= hill_A2000EsppMember
Expected Term 6 months 6 months 6 months
Forfeiture Rate 0.00%hill_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsForfeitureRate
/ us-gaap_PlanNameAxis
= hill_A2000EsppMember
0.00%hill_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsForfeitureRate
/ us-gaap_PlanNameAxis
= hill_A2000EsppMember
0.00%hill_ShareBasedCompensationArrangementByShareBasedPaymentAwardFairValueAssumptionsForfeitureRate
/ us-gaap_PlanNameAxis
= hill_A2000EsppMember