Income Taxes - Unrecognized tax benefits (Details) - USD ($) $ in Thousands		3 Months Ended	12 Months Ended
	Jan. 01, 2018	Mar. 31, 2019	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Income Tax Disclosure [Abstract]
Statutory federal rate	21.00%		21.00%	21.00%	21.00%
Deferred tax asset adjustment						$ 11,400
Tax benefit					$ 1,200
Deferred tax assets		$ 11,500
Deferred tax assets, valuation allowance			$ 0	$ 4,694
Tax expense (benefits) related to interest and penalties			64	145
Amount of interest and penalties			45	119
Unrecognized tax benefits			200
Income taxes paid			45,400	48,800	13,400
Reconciliation of the beginning and ending amount of unrecognized tax benefits
Beginning unrecognized tax benefits		$ 624	1,165	624
Additions for tax positions taken in the prior year			30	845
Reductions for tax positions taken in prior years			(881)	(304)
Ending unrecognized tax benefits			$ 314	$ 1,165	$ 624