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Investments - Additional Information (Detail) (USD $)
In Thousands, unless otherwise specified
 12 Months Ended
Dec. 31, 2014
Dec. 31, 2013
Dec. 31, 2012
Dec. 31, 2011
Schedule of Trading Securities and Other Trading Assets [Line Items]        
Unrealized gain, net of other expenses $ 237us-gaap_TradingSecuritiesUnrealizedHoldingGainLoss $ 489us-gaap_TradingSecuritiesUnrealizedHoldingGainLoss $ 451us-gaap_TradingSecuritiesUnrealizedHoldingGainLoss  
Investments in equity securities        
Schedule of Trading Securities and Other Trading Assets [Line Items]        
Trading Securities, Realized Gain   702us-gaap_TradingSecuritiesRealizedGain
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_EquitySecuritiesMember		    
Trading Securities, Unrealized Holding Gain   $ 438us-gaap_TradingSecuritiesUnrealizedHoldingGain
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_EquitySecuritiesMember		 $ 135us-gaap_TradingSecuritiesUnrealizedHoldingGain
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_EquitySecuritiesMember		 $ 304us-gaap_TradingSecuritiesUnrealizedHoldingGain
/ us-gaap_MajorTypesOfDebtAndEquitySecuritiesAxis
= us-gaap_EquitySecuritiesMember