Schedule II - Valuation and Qualifying Accounts - Summary of Valuation Allowance (Details) - USD ($) $ in Thousands		12 Months Ended
		Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
SEC Schedule, 12-09, Allowance, Credit Loss [Member]
Allowance for doubtful accounts		$ 4,606	$ 3,163	$ 1,794
Allowance for doubtful accounts		2,171	2,400	1,917
Allowance for doubtful accounts	[1]	0		167
Allowance for doubtful accounts	[2]	(1,431)	(957)	(715)
Allowance for doubtful accounts		5,346	4,606	3,163
SEC Schedule, 12-09, Valuation Allowance, Deferred Tax Asset [Member]
Allowance for doubtful accounts		75	1,532	1,683
Allowance for doubtful accounts		(75)	(1,457)	0
Allowance for doubtful accounts	[1]	0	0	0
Allowance for doubtful accounts	[2]	0		(151)
Allowance for doubtful accounts			$ 75	$ 1,532

[1] In 2016, the change in the allowance for doubtful accounts represents the fair value of balances assumed in acquisition transactions. See Note 3 Acquisitions and Dispositions of the notes to our audited consolidated financial statements included elsewhere herein for further information.

[2] Deductions from allowance for doubtful accounts represent write-offs of receivable balances not considered collectible. The deduction from the valuation allowance for deferred tax assets represents changes in estimates of our future taxable income and our estimated future usage of certain net operating loss carryforwards, as well as expiration of certain net operating loss carryforwards.