Income Taxes - Rollforward of Unrecognized Tax Benefits (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]
Beginning balance		$ 16,248	$ 2,039	$ 1,408
Additions for tax positions relating to the current year		1,209	845	640
Additions for tax positions relating to prior years		582	13,389	0
Reductions for tax positions relating to prior years		(60)	(25)	(9)
Reductions for settlements with taxing authorities		(1,629)	0	0
Ending balance		16,350	16,248	2,039
Interest and penalties not included above:
Interest expense, net of tax effect, and penalties	[1]	(21)	118	49
Accrued interest and penalties, net of tax effect, at end of year	[1]	$ 170	$ 191	$ 73

[1] Included in income tax expense in the Consolidated Statements of Income.