Income Taxes (Details 3) (USD $)	6 Months Ended
	Jun. 30, 2014	Jun. 30, 2013
Income Taxes
Excess tax benefit from exercise of stock options	$ 854,000	$ 4,200,000
Net unrecognized tax benefits	1,600,000	1,200,000
Accrued liabilities for interest expense and penalties related to unrecognized tax benefits	$ 1,200,000	$ 900,000