Summary of Significant Accounting Policies - Summary of Impacts of Adopting ASC 606 on Condensed Statement of Cash Flows (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2018	Mar. 31, 2017
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Net income	$ 14,014	$ 20,237
Adjustments to reconcile net income to net cash provided by operating activities-
Amortization	9,946	7,471
Deferred income taxes	4,017	5,971
Other	10,270
Changes in operating assets and liabilities:
Other current and non-current assets	(4,629)	2,793
Deferred revenue	(3,331)	5,661
Other	(432)
Net cash provided by operating activities	29,855	29,964
Cash flows from investing activities:
Acquisition of and investments in client contracts		(4,363)
Other	(16,433)
Net cash provided by (used in) investing activities	(16,433)	5,879
Net cash provided by financing activities	9,685	(56,393)
Effect of exchange rate fluctuations on cash	2,153	1,621
Net increase (decrease) in cash and cash equivalents	25,260	(18,929)
Cash and cash equivalents, beginning of period	122,243	126,351
Cash and cash equivalents, end of period	147,503	$ 107,422
Adjustments | ASU 606
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Net income	457
Adjustments to reconcile net income to net cash provided by operating activities-
Amortization	(878)
Deferred income taxes	187
Changes in operating assets and liabilities:
Other current and non-current assets	2,298
Deferred revenue	(563)
Net cash provided by operating activities	1,501
Cash flows from investing activities:
Acquisition of and investments in client contracts	(1,501)
Net cash provided by (used in) investing activities	(1,501)
Balances without Adoption of ASC 606 | ASU 606
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Net income	14,471
Adjustments to reconcile net income to net cash provided by operating activities-
Amortization	9,068
Deferred income taxes	4,204
Other	10,270
Changes in operating assets and liabilities:
Other current and non-current assets	(2,331)
Deferred revenue	(3,894)
Other	(432)
Net cash provided by operating activities	31,356
Cash flows from investing activities:
Acquisition of and investments in client contracts	(1,501)
Other	(16,433)
Net cash provided by (used in) investing activities	(17,934)
Net cash provided by financing activities	9,685
Effect of exchange rate fluctuations on cash	2,153
Net increase (decrease) in cash and cash equivalents	25,260
Cash and cash equivalents, beginning of period	122,243
Cash and cash equivalents, end of period	$ 147,503