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Fair Value Measurement - Cash and Cash Equivalents (Details) (USD $)
In Thousands, unless otherwise specified
Mar. 31, 2015
Dec. 31, 2014
Mar. 31, 2014
Dec. 31, 2013
Cash Equivalents, at Carrying Value [Abstract]        
Cash equivalents $ 54,709us-gaap_MoneyMarketFundsAtCarryingValue $ 60,618us-gaap_MoneyMarketFundsAtCarryingValue $ 49,770us-gaap_MoneyMarketFundsAtCarryingValue  
Cash 184,694gva_Cash1 195,343gva_Cash1 156,010gva_Cash1  
Total cash and cash equivalents $ 239,403us-gaap_CashAndCashEquivalentsAtCarryingValue $ 255,961us-gaap_CashAndCashEquivalentsAtCarryingValue $ 205,780us-gaap_CashAndCashEquivalentsAtCarryingValue $ 229,121us-gaap_CashAndCashEquivalentsAtCarryingValue