Business Combinations - Assets Acquired and Liabilities & Equity Assumed (Details) - USD ($) $ in Thousands	Dec. 31, 2019	Dec. 31, 2018	Jul. 01, 2018	Dec. 31, 2017	Dec. 31, 2016
Assets:
Goodwill	$ 290,366	$ 290,366		$ 170,153	$ 6,788
Sustainable Growth Advisers, LP
Assets:
Cash and cash equivalents			$ 2,505
Investments			262
Accounts receivable			6,649
Furniture, equipment and leasehold improvements			70
Intangible assets			62,000
Goodwill			120,213
Other assets			659
Total Assets			192,358
Liabilities:
Accrued compensation and benefits			824
Accounts payable and accrued liabilities			6,534
Total liabilities			7,358
Redeemable noncontrolling interests			55,500
Total Net Assets Acquired			$ 129,500