Income Taxes - Uncertain Tax Positions (Details) - USD ($) $ in Thousands	12 Months Ended
Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Reconciliation of Unrecognized Tax Benefits, Excluding Amounts Pertaining to Examined Tax Returns [Roll Forward]
Gross unrecognized tax benefits—beginning balance	$ 48,835	$ 26,915	$ 22,239
Increases related to tax positions taken in a prior year	330	1,243	46
Increases related to tax positions taken during current year	27,413	22,202	11,359
Decreases related to tax positions taken in a prior year	(675)	(21)	(426)
Decreases related to settlements with taxing authorities	0	0	(432)
Decreases related to lapse of statute of limitations	(2,173)	(1,504)	(5,871)
Adjustment for acquisition	706	0	0
Gross unrecognized tax benefits—ending balance	$ 74,436	$ 48,835	$ 26,915

A roll forward is a reconciliation of a concept from the beginning of a period to the end of a period.

No definition available.

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Amount of unrecognized tax benefits.

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