Accumulated Other Comprehensive Loss - Components of Accumulated Other Comprehensive Loss, Net of Tax (Details) $ in Thousands	6 Months Ended
	Jun. 30, 2019 USD ($)
Accumulated Other Comprehensive Income Loss [Line Items]
Balance at December 31, 2018	$ (361,888)
Balance at June 30, 2019	(377,500)
Foreign Currency Translation Adjustments [Member]
Accumulated Other Comprehensive Income Loss [Line Items]
Balance at December 31, 2018	1,273
Net current period other comprehensive income	202
Reclassifications	0
Balance at June 30, 2019	1,475
Net Unrealized Gains on Marketable Securities [Member]
Accumulated Other Comprehensive Income Loss [Line Items]
Balance at December 31, 2018	(10)
Net current period other comprehensive income	(209)
Reclassifications	0
Balance at June 30, 2019	(219)
Accumulated Other Comprehensive Loss (Income) [Member]
Accumulated Other Comprehensive Income Loss [Line Items]
Balance at December 31, 2018	1,263
Net current period other comprehensive income	(7)
Reclassifications	0
Balance at June 30, 2019	$ 1,256