Segment Reporting and Significant Concentration - Summary of Financial Information Relating to Operations by Geographic Region (Details) - USD ($) $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2019	Sep. 30, 2019	Jun. 30, 2019	Mar. 31, 2019	Dec. 31, 2018	Sep. 30, 2018	Jun. 30, 2018	Mar. 31, 2018	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Total Revenues:
Total revenues	$ 254,747	$ 251,414	$ 245,856	$ 244,793	$ 247,267	$ 213,055	$ 213,033	$ 201,704	$ 996,810	$ 875,059	$ 789,582
Property and Equipment:
Property and Equipment	84,429				81,813				84,429	81,813
Americas (principally the U.S.)
Total Revenues:
Total revenues									866,831	740,885	669,712
Property and Equipment:
Property and Equipment	70,990				72,079				70,990	72,079
Europe, Middle East and Africa (principally Europe)
Total Revenues:
Total revenues									91,685	89,924	72,120
Property and Equipment:
Property and Equipment	1,564				2,056				1,564	2,056
Asia Pacific
Total Revenues:
Total revenues									38,294	44,250	$ 47,750
Property and Equipment:
Property and Equipment	$ 11,875				$ 7,678				$ 11,875	$ 7,678