Significant Accounting Policies - Recent Accounting Pronouncements (Details) - USD ($) $ in Thousands |
3 Months Ended | 9 Months Ended | |||
|---|---|---|---|---|---|
Sep. 30, 2018 |
Sep. 30, 2017 |
Sep. 30, 2018 |
Sep. 30, 2017 |
Jan. 01, 2018 |
|
| Recent Accounting Pronouncements | |||||
| Fund administration and distribution fees | $ 15,557 | $ 16,372 | $ 46,792 | $ 49,378 | |
| Cumulative effect adjustment for adoption of ASU 2016-09 | 1,818 | 1,818 | |||
| Distribution Fee Revenue | |||||
| Recent Accounting Pronouncements | |||||
| Fund administration and distribution fees | $ 9,400 | $ 10,700 | $ 29,100 | $ 32,900 | |
| ASU 2016-09 | |||||
| Recent Accounting Pronouncements | |||||
| Cumulative effect adjustment for adoption of ASU 2016-09 | $ 1,300 | ||||