Income Taxes (Details) (USD $)	6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013
Income Taxes
Effective income tax rate (as a percent)	42.60%	39.30%
Excess tax benefit from exercise of stock options	$ 854,000	$ 4,200,000
Net unrecognized tax benefits	1,600,000	1,200,000
Unrecognized tax benefits with impact to the effective tax rate	200,000	100,000
Accrued liabilities for interest expense and penalties related to unrecognized tax benefits	$ 1,200,000	$ 900,000