Credit Agreement - Additional Information (Details) (USD $)	12 Months Ended
	Dec. 31, 2014	Sep. 30, 2013	Nov. 05, 2014	Nov. 04, 2014
Line of Credit [Member] | Revolving Credit Facility [Member] | Wells Fargo Bank, National Association [Member]
Debt Instrument [Line Items]
Revolving credit facility with a letter of credit sub limit		$ 75,000,000
Line of Credit [Member] | Letter of Credit [Member] | Wells Fargo Bank, National Association [Member]
Debt Instrument [Line Items]
Revolving credit facility with a letter of credit sub limit		10,000,000
Increases in to aggregate commitments (does not exceed $25 million)		25,000,000
Commitment fee percentage	0.25%
Eurodollar [Member] | Line of Credit [Member] | Letter of Credit [Member] | Wells Fargo Bank, National Association [Member]
Debt Instrument [Line Items]
Amounts draw under the Credit Agreements bears interest rate	1.75%
Federal Funds Effective Swap Rate [Member] | Line of Credit [Member] | Letter of Credit [Member] | Wells Fargo Bank, National Association [Member]
Debt Instrument [Line Items]
Amounts draw under the Credit Agreements bears interest rate	0.50%
London Interbank Offered Rate (LIBOR) [Member] | Line of Credit [Member] | Letter of Credit [Member] | Wells Fargo Bank, National Association [Member]
Debt Instrument [Line Items]
Amounts draw under the Credit Agreements bears interest rate	1.75%
November 2014 Stock Repurchase Program [Member]
Debt Instrument [Line Items]
Authorized amount of repurchase of common stock			$ 50,000,000	$ 25,000,000