Income Taxes - Unrecognized Tax Benefits Reconciliation (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Unrecognized Tax Benefits Reconciliation
Balance at beginning of year	$ 24,361	$ 31,534	$ 36,935
Additions based on tax positions taken during a prior period	583	2,342	2,356
Reductions based on tax positions taken during a prior period	(1,248)	(1,242)	(6,305)
Additions related to positions taken upon finalization of Tax Act during the current period	16,506	0	0
Additions based on tax positions taken during the current period	3,133	6,543	3,935
Reductions based on tax positions taken during the current period	(233)	0	0
Reductions related to settlement of tax matters	(136)	(2,921)	(2,795)
Reductions related to a lapse of applicable statute of limitations	(7,087)	(11,895)	(2,592)
Balance at end of year	35,879	24,361	$ 31,534
Unrecognized Tax Benefits, Income Tax Penalties and Interest Accrued	$ 4,189	$ 3,301