Income Taxes - Deferred tax assets and liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018
Deferred tax assets:
Lease liabilities	$ 31,432
Provision for doubtful accounts and implicit price	18,547	$ 16,529
Accrued expenses	12,789	15,352
Property, plant and equipment	9,797	10,829
Interest expense	8,946	7,798
Deferred benefit plan compensation	8,834	6,269
Net operating loss carryforwards	7,636	10,975
Share based compensation	4,016	3,902
Inventory reserves	2,554	2,710
Refund liabilities	2,346	2,517
Intangibles	1,236	1,063
Interest on seller notes	961	1,029
Deferred rent		1,136
Other	893	1,307
Deferred tax assets	109,987	81,416
Less: Valuation allowance	(2,065)	(8,930)
Total deferred tax assets	107,922	72,486
Deferred tax liabilities:
Lease assets	28,360
Goodwill	7,960	5,821
Prepaid expenses	1,121	1,030
Total deferred tax liabilities	37,441	6,851
Net deferred tax asset	$ 70,481	$ 65,635