Income Taxes - Unrealized benefits (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Income Tax Disclosure [Abstract]
Deferred tax asset not recognized for excess equity compensation	$ 5,400
Non-current liability related to uncertain tax positions	0
Reconciliation of the gross unrealized tax benefits
Unrecognized tax benefits, beginning of year	4,052	$ 2,794	$ 1,674
Gross increases - tax positions from prior periods	43		10
Gross increases - tax positions from current period	1,211	1,258	1,110
Unrecognized tax benefits, end of year	$ 5,306	$ 4,052	$ 2,794