Income Taxes (Details) (USD $)	9 Months Ended
	Sep. 30, 2014	Sep. 30, 2013
Income Taxes
Effective income tax rate (as a percent)	42.40%	39.40%
Excess tax benefit from exercise of stock options	$ 870,000	$ 5,200,000
Net unrecognized tax benefits	1,600,000	1,400,000
Unrecognized tax benefits with impact to the effective tax rate	1,100,000	900,000
Accrued liabilities for interest expense and penalties related to unrecognized tax benefits	$ 300,000	$ 200,000