Segment Information (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Revenues	$ 346,059	$ 292,724	$ 287,889	$ 280,623	$ 316,380	$ 273,616	$ 273,174	$ 254,669	$ 1,207,295	$ 1,117,838	$ 874,255
Total long-lived assets	593,595				532,714				593,595	532,714
United States
Revenues									924,051	830,800	607,285
Total long-lived assets	530,785				452,143				530,785	452,143
Canada
Revenues									73,742	78,099	76,775
Ireland
Revenues									69,291	74,430	71,340
All other countries
Revenues									140,211	134,509	$ 118,855
Total long-lived assets	$ 62,810				$ 80,571				$ 62,810	$ 80,571