Income Taxes (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014
Income Taxes
Effective income tax rate (as a percent)	44.80%	43.20%	43.60%	42.60%
Discrete tax expense due to change in tax laws	$ 600		$ 600
Discrete tax rate changes due to change in tax laws (as a percent)	6.00%		3.70%
Excess tax benefit from exercise of stock options			$ 1,456
Tax deductions arising from stock-based compensation				$ 3,900
Net unrecognized tax benefits	$ 1,400	$ 1,600	1,400	1,600
Accrued liabilities for interest expense and penalties related to unrecognized tax benefits	$ 400	$ 200	$ 400	$ 200