Summary of Significant Accounting Policies - Summary of Impacts of Adopting ASC 606 on Condensed Statement of Cash Flows (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Net income	$ 66,130	$ 61,364	$ 62,882
Adjustments to reconcile net income to net cash provided by operating activities-
Amortization	44,328	29,501	27,626
Deferred income taxes	4,913	7,112	(2,811)
Other	44,146
Changes in operating assets and liabilities:
Other current and non-current assets	(23,179)
Deferred revenue	10,492	(300)	957
Other	(3,489)
Net cash provided by operating activities	143,341	127,195	84,186
Cash flows from investing activities:
Acquisition of and investments in client contracts		(12,180)	(7,587)
Other	(86,139)
Net cash used in investing activities	(86,139)	(29,904)	(52,142)
Net cash used in financing activities	(37,509)	(105,494)	$ (42,950)
Effect of exchange rate fluctuations on cash	(2,659)
Net increase cash and cash equivalents	17,034
Cash and cash equivalents, beginning of period	122,243
Cash and cash equivalents, end of period	139,277	122,243
Adjustments | ASC 606
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Net income	1,568
Adjustments to reconcile net income to net cash provided by operating activities-
Amortization	(4,202)
Deferred income taxes	640
Changes in operating assets and liabilities:
Other current and non-current assets	13,183
Deferred revenue	(1,881)
Net cash provided by operating activities	9,308
Cash flows from investing activities:
Acquisition of and investments in client contracts	(9,308)
Net cash used in investing activities	(9,308)
Balances without Adoption of ASC 606 | ASC 606
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Net income	67,698
Adjustments to reconcile net income to net cash provided by operating activities-
Amortization	40,126
Deferred income taxes	5,553
Other	44,146
Changes in operating assets and liabilities:
Other current and non-current assets	(9,996)
Deferred revenue	8,611
Other	(3,489)
Net cash provided by operating activities	152,649
Cash flows from investing activities:
Acquisition of and investments in client contracts	(9,308)
Other	(86,139)
Net cash used in investing activities	(95,447)
Net cash used in financing activities	(37,509)
Effect of exchange rate fluctuations on cash	(2,659)
Net increase cash and cash equivalents	17,034
Cash and cash equivalents, beginning of period	122,243
Cash and cash equivalents, end of period	$ 139,277	$ 122,243