Income Taxes (Details 2) (USD $)	3 Months Ended
	Mar. 31, 2014	Mar. 31, 2013
Income Taxes
Excess tax benefit from exercise of stock options	$ 854,000	$ 3,000,000
Net unrecognized tax benefits	1,500,000	1,100,000
Unrecognized tax benefits net of the federal benefit for state issues	100,000	100,000
Accrued liabilities for interest expense and penalties related to unrecognized tax benefits	$ 1,100,000	$ 900,000