Income Taxes (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2019	Mar. 31, 2018	Dec. 31, 2018
Income Taxes
Income tax provision	$ 472	$ 3,558
Decrease in income tax		3,100
Decrease in income tax due to decrease in pretax income		2,300
Decrease in pretax income		10,900
Decrease in income tax due to increase in excess tax benefit on exercise of stock options and vesting of restricted stock		300
Decrease in income tax due to tax benefit recognized upon expiration of statute of limitation regarding uncertain tax position previously recorded		300
Interest and penalties previously accrued credited to interest expenses		$ 100
Deferred tax assets valuation allowance			$ 71,900