Segment and Geographic Information (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017	Dec. 31, 2017
Total revenues	$ 287,889	$ 273,174	$ 568,512	$ 527,843
United States	533,211		533,211		$ 532,714
Total long-lived assets	533,211		533,211		532,714
UNITED STATES
Total revenues	218,996	202,493	428,072	388,255
United States	463,582		463,582		452,143
Total long-lived assets	463,582		463,582		452,143
CANADA
Total revenues	18,528	19,351	38,150	38,752
IRELAND
Total revenues	17,013	18,479	34,114	36,380
All Other Countries [Member]
Total revenues	33,352	$ 32,851	68,176	$ 64,456
United States	69,629		69,629		80,571
Total long-lived assets	$ 69,629		$ 69,629		$ 80,571