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		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Net income	$ 15,117	$ 11,581	$ 29,131	$ 31,818
Adjustments to reconcile net income to net cash provided by operating activities-
Amortization			20,957	14,418
Deferred income taxes			4,944	1,725
Other			21,691
Changes in operating assets and liabilities:
Other current and non-current assets			(13,995)	(4,787)
Deferred revenue			799	12,288
Other			(37,313)
Net cash provided by operating activities			26,214	64,488
Cash flows from investing activities:
Acquisition of and investments in client contracts				(7,526)
Other			(22,830)
Net cash provided by (used in) investing activities			(22,830)	4,196
Net cash used in financing activities			(4,925)	$ (71,620)
Effect of exchange rate fluctuations on cash			(1,031)
Net decrease cash and cash equivalents			(2,572)
Cash and cash equivalents, beginning of period			122,243
Cash and cash equivalents, end of period	119,671		119,671
Adjustments | ASC 606
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Net income	459		916
Adjustments to reconcile net income to net cash provided by operating activities-
Amortization			(2,002)
Deferred income taxes			374
Changes in operating assets and liabilities:
Other current and non-current assets			5,349
Deferred revenue			(1,126)
Net cash provided by operating activities			3,511
Cash flows from investing activities:
Acquisition of and investments in client contracts			(3,511)
Net cash provided by (used in) investing activities			(3,511)
Balances without Adoption of ASC 606 | ASC 606
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Net income	15,576		30,047
Adjustments to reconcile net income to net cash provided by operating activities-
Amortization			18,955
Deferred income taxes			5,318
Other			21,691
Changes in operating assets and liabilities:
Other current and non-current assets			(8,646)
Deferred revenue			(327)
Other			(37,313)
Net cash provided by operating activities			29,725
Cash flows from investing activities:
Acquisition of and investments in client contracts			(3,511)
Other			(22,830)
Net cash provided by (used in) investing activities			(26,341)
Net cash used in financing activities			(4,925)
Effect of exchange rate fluctuations on cash			(1,031)
Net decrease cash and cash equivalents			(2,572)
Cash and cash equivalents, beginning of period			122,243
Cash and cash equivalents, end of period	$ 119,671		$ 119,671