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Revenues from Contracts with Customers (Details) - USD ($) | 3 Months Ended | 12 Months Ended |
--- | --- | --- | ---
Dec. 31, 2018 | Sep. 30, 2018 | Jun. 30, 2018 | Mar. 31, 2018 | Dec. 31, 2017 | Sep. 30, 2017 | Jun. 30, 2017 | Mar. 31, 2017 | Dec. 31, 2018 | Dec. 31, 2017 | Dec. 31, 2016 | Jan. 01, 2018
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Revenues | $ 405,057,000 | $ 408,682,000 | $ 404,830,000 | $ 405,598,000 | $ 408,219,000 | $ 386,018,000 | $ 372,331,000 | $ 359,984,000 | $ 1,624,167,000 | $ 1,526,552,000 | $ 1,401,545,000 |
Deferred contract costs | $ 24,007,000 |  |  |  | $ 0 |  |  |  | 24,007,000 | 0 |  |
Capitalized contract cost, amount capitalized during period |  |  |  |  |  |  |  |  | 8,122,000 |  |  |
Amortization of deferred contract costs |  |  |  |  |  |  |  |  | 2,756,000 |  |  |
Capitalized contract cost impairment |  |  |  |  |  |  |  |  | 0 |  |  |
United States |  |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Revenues |  |  |  |  |  |  |  |  | 1,348,130,000 | 1,298,381,000 | 1,191,640,000 |
United Kingdom |  |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Revenues |  |  |  |  |  |  |  |  | 168,451,000 |  |  |
Canada |  |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Revenues |  |  |  |  |  |  |  |  | 54,467,000 |  |  |
Ireland |  |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Revenues |  |  |  |  |  |  |  |  | 51,316,000 |  |  |
Other |  |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Revenues |  |  |  |  |  |  |  |  | 1,803,000 |  |  |
Investment management fees from pooled investment products |  |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Revenues |  |  |  |  |  |  |  |  | 488,330,000 |  |  |
Investment management fees from investment management agreements |  |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Revenues |  |  |  |  |  |  |  |  | 376,707,000 |  |  |
Investment operations fees |  |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Revenues |  |  |  |  |  |  |  |  | 361,899,000 |  |  |
Investment processing fees - PaaS |  |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Revenues |  |  |  |  |  |  |  |  | 184,587,000 |  |  |
Investment processing fees - SaaS |  |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Revenues |  |  |  |  |  |  |  |  | 145,820,000 |  |  |
Professional services fees |  |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Revenues |  |  |  |  |  |  |  |  | 23,923,000 |  |  |
Account fees and other |  |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Revenues |  |  |  |  |  |  |  |  | 42,901,000 |  |  |
Private Banks |  |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Revenues |  |  |  |  |  |  |  |  | 483,097,000 | 474,272,000 | 457,886,000 |
Private Banks | United States |  |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Revenues |  |  |  |  |  |  |  |  | 304,762,000 |  |  |
Private Banks | United Kingdom |  |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Revenues |  |  |  |  |  |  |  |  | 112,980,000 |  |  |
Private Banks | Canada |  |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Revenues |  |  |  |  |  |  |  |  | 45,941,000 |  |  |
Private Banks | Ireland |  |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Revenues |  |  |  |  |  |  |  |  | 19,414,000 |  |  |
Private Banks | Other |  |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Revenues |  |  |  |  |  |  |  |  | 0 |  |  |
Private Banks | Investment management fees from pooled investment products |  |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Revenues |  |  |  |  |  |  |  |  | 138,616,000 |  |  |
Private Banks | Investment management fees from investment management agreements |  |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Revenues |  |  |  |  |  |  |  |  | 793,000 |  |  |
Private Banks | Investment operations fees |  |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Revenues |  |  |  |  |  |  |  |  | 1,517,000 |  |  |
Private Banks | Investment processing fees - PaaS |  |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Revenues |  |  |  |  |  |  |  |  | 182,068,000 |  |  |
Private Banks | Investment processing fees - SaaS |  |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Revenues |  |  |  |  |  |  |  |  | 136,222,000 |  |  |
Private Banks | Professional services fees |  |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Revenues |  |  |  |  |  |  |  |  | 16,643,000 |  |  |
Private Banks | Account fees and other |  |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Revenues |  |  |  |  |  |  |  |  | 7,238,000 |  |  |
Investment Advisors |  |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Revenues |  |  |  |  |  |  |  |  | 399,089,000 | 373,473,000 | 330,677,000 |
Investment Advisors | United States |  |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Revenues |  |  |  |  |  |  |  |  | 399,089,000 |  |  |
Investment Advisors | United Kingdom |  |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Revenues |  |  |  |  |  |  |  |  | 0 |  |  |
Investment Advisors | Canada |  |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Revenues |  |  |  |  |  |  |  |  | 0 |  |  |
Investment Advisors | Ireland |  |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Revenues |  |  |  |  |  |  |  |  | 0 |  |  |
Investment Advisors | Other |  |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Revenues |  |  |  |  |  |  |  |  | 0 |  |  |
Investment Advisors | Investment management fees from pooled investment products |  |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Revenues |  |  |  |  |  |  |  |  | 288,030,000 |  |  |
Investment Advisors | Investment management fees from investment management agreements |  |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Revenues |  |  |  |  |  |  |  |  | 94,526,000 |  |  |
Investment Advisors | Investment operations fees |  |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Revenues |  |  |  |  |  |  |  |  | 0 |  |  |
Investment Advisors | Investment processing fees - PaaS |  |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Revenues |  |  |  |  |  |  |  |  | 0 |  |  |
Investment Advisors | Investment processing fees - SaaS |  |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Revenues |  |  |  |  |  |  |  |  | 0 |  |  |
Investment Advisors | Professional services fees |  |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Revenues |  |  |  |  |  |  |  |  | 0 |  |  |
Investment Advisors | Account fees and other |  |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Revenues |  |  |  |  |  |  |  |  | 16,533,000 |  |  |
Institutional Investors |  |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Revenues |  |  |  |  |  |  |  |  | 333,299,000 | 322,457,000 | 312,584,000 |
Institutional Investors | United States |  |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Revenues |  |  |  |  |  |  |  |  | 257,080,000 |  |  |
Institutional Investors | United Kingdom |  |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Revenues |  |  |  |  |  |  |  |  | 55,471,000 |  |  |
Institutional Investors | Canada |  |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Revenues |  |  |  |  |  |  |  |  | 8,526,000 |  |  |
Institutional Investors | Ireland |  |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Revenues |  |  |  |  |  |  |  |  | 10,419,000 |  |  |
Institutional Investors | Other |  |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Revenues |  |  |  |  |  |  |  |  | 1,803,000 |  |  |
Institutional Investors | Investment management fees from pooled investment products |  |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Revenues |  |  |  |  |  |  |  |  | 59,739,000 |  |  |
Institutional Investors | Investment management fees from investment management agreements |  |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Revenues |  |  |  |  |  |  |  |  | 271,600,000 |  |  |
Institutional Investors | Investment operations fees |  |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Revenues |  |  |  |  |  |  |  |  | 0 |  |  |
Institutional Investors | Investment processing fees - PaaS |  |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Revenues |  |  |  |  |  |  |  |  | 0 |  |  |
Institutional Investors | Investment processing fees - SaaS |  |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Revenues |  |  |  |  |  |  |  |  | 0 |  |  |
Institutional Investors | Professional services fees |  |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Revenues |  |  |  |  |  |  |  |  | 0 |  |  |
Institutional Investors | Account fees and other |  |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Revenues |  |  |  |  |  |  |  |  | 1,960,000 |  |  |
Investment Managers |  |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Revenues |  |  |  |  |  |  |  |  | 398,076,000 | 349,444,000 | 294,390,000 |
Investment Managers | United States |  |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Revenues |  |  |  |  |  |  |  |  | 376,593,000 |  |  |
Investment Managers | United Kingdom |  |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Revenues |  |  |  |  |  |  |  |  | 0 |  |  |
Investment Managers | Canada |  |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Revenues |  |  |  |  |  |  |  |  | 0 |  |  |
Investment Managers | Ireland |  |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Revenues |  |  |  |  |  |  |  |  | 21,483,000 |  |  |
Investment Managers | Other |  |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Revenues |  |  |  |  |  |  |  |  | 0 |  |  |
Investment Managers | Investment management fees from pooled investment products |  |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Revenues |  |  |  |  |  |  |  |  | 928,000 |  |  |
Investment Managers | Investment management fees from investment management agreements |  |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Revenues |  |  |  |  |  |  |  |  | 331,000 |  |  |
Investment Managers | Investment operations fees |  |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Revenues |  |  |  |  |  |  |  |  | 360,382,000 |  |  |
Investment Managers | Investment processing fees - PaaS |  |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Revenues |  |  |  |  |  |  |  |  | 2,519,000 |  |  |
Investment Managers | Investment processing fees - SaaS |  |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Revenues |  |  |  |  |  |  |  |  | 9,598,000 |  |  |
Investment Managers | Professional services fees |  |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Revenues |  |  |  |  |  |  |  |  | 7,280,000 |  |  |
Investment Managers | Account fees and other |  |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Revenues |  |  |  |  |  |  |  |  | 17,038,000 |  |  |
Investments In New Businesses |  |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Revenues |  |  |  |  |  |  |  |  | 10,606,000 | $ 6,906,000 | $ 6,008,000 |
Investments In New Businesses | United States |  |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Revenues |  |  |  |  |  |  |  |  | 10,606,000 |  |  |
Investments In New Businesses | United Kingdom |  |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Revenues |  |  |  |  |  |  |  |  | 0 |  |  |
Investments In New Businesses | Canada |  |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Revenues |  |  |  |  |  |  |  |  | 0 |  |  |
Investments In New Businesses | Ireland |  |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Revenues |  |  |  |  |  |  |  |  | 0 |  |  |
Investments In New Businesses | Other |  |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Revenues |  |  |  |  |  |  |  |  | 0 |  |  |
Investments In New Businesses | Investment management fees from pooled investment products |  |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Revenues |  |  |  |  |  |  |  |  | 1,017,000 |  |  |
Investments In New Businesses | Investment management fees from investment management agreements |  |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Revenues |  |  |  |  |  |  |  |  | 9,457,000 |  |  |
Investments In New Businesses | Investment operations fees |  |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Revenues |  |  |  |  |  |  |  |  | 0 |  |  |
Investments In New Businesses | Investment processing fees - PaaS |  |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Revenues |  |  |  |  |  |  |  |  | 0 |  |  |
Investments In New Businesses | Investment processing fees - SaaS |  |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Revenues |  |  |  |  |  |  |  |  | 0 |  |  |
Investments In New Businesses | Professional services fees |  |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Revenues |  |  |  |  |  |  |  |  | 0 |  |  |
Investments In New Businesses | Account fees and other |  |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Revenues |  |  |  |  |  |  |  |  | $ 132,000 |  |  |
Retained Earnings | Accounting Standards Update 2014-09 |  |  |  |  |  |  |  |  |  |  |  |
Disaggregation of Revenue [Line Items] |  |  |  |  |  |  |  |  |  |  |  |
Cumulative effect adjustment, before tax |  |  |  |  |  |  |  |  |  |  |  | $ 18,641,000

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- Definition Capitalized Contract Cost, Amount Capitalized During Period + References No definition available. + Details
Name: | seic_CapitalizedContractCostAmountCapitalizedDuringPeriod
Namespace Prefix: | seic_
Data Type: | xbrli:monetaryItemType
Balance Type: | debit
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