Fair Value Measurement (Details) (USD $)	3 Months Ended	12 Months Ended
	Mar. 31, 2015	Dec. 31, 2014
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Auction rate security bond par value	$ 1,000,000	$ 1,000,000
Percentage of auction rate security guaranteed	97.00%	97.00%
Minimum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Percentage of carrying value of auction rate securities	0.00%	0.00%
Maximum
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Percentage of carrying value of auction rate securities	4.00%	4.00%