Accumulated Other Comprehensive Loss - Components of Accumulated Other Comprehensive Loss, Net of Tax (Details) $ in Thousands	3 Months Ended
	Mar. 31, 2019 USD ($)
Accumulated Other Comprehensive Income Loss [Line Items]
Balance at December 31, 2018	$ (361,888)
Balance at March 31, 2019	(369,862)
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	518
Reclassifications	0
Balance at March 31, 2019	1,791
Net Unrealized (Gains) Losses on Marketable Securities [Member]
Accumulated Other Comprehensive Income Loss [Line Items]
Balance at December 31, 2018	(10)
Net current period other comprehensive income	(95)
Reclassifications	0
Balance at March 31, 2019	(105)
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	423
Reclassifications	0
Balance at March 31, 2019	$ 1,686