Segment Reporting and Foreign Operations - Long-lived Assets by Geographic Area (Details) - USD ($) $ in Thousands	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Revenues from External Customers and Long-Lived Assets [Line Items]
Long-lived assets	$ 292,820	$ 276,573	$ 267,778
United States
Revenues from External Customers and Long-Lived Assets [Line Items]
Long-lived assets	202,504	194,715	186,389
Ireland
Revenues from External Customers and Long-Lived Assets [Line Items]
Long-lived assets	45,671	47,337	48,896
Other foreign countries
Revenues from External Customers and Long-Lived Assets [Line Items]
Long-lived assets	$ 44,645	$ 34,521	$ 32,493