Subordinated Debt - Schedule of Subordinated Debt (Details) - USD ($) $ in Thousands	Jun. 30, 2021	Dec. 31, 2020
Debt Instrument [Line Items]
Principal	$ 514,919	$ 514,916
Unamortized Debt Issuance Costs	(2,129)	(2,397)
Subordinated Debt
Debt Instrument [Line Items]
Principal	72,000	82,000
Unamortized Debt Issuance Costs	(2,129)	(2,397)
Subordinated Debt | 2025 Note
Debt Instrument [Line Items]
Principal	0	10,000
Unamortized Debt Issuance Costs	0	(114)
Subordinated Debt | 2026 Notes
Debt Instrument [Line Items]
Principal	25,000	25,000
Unamortized Debt Issuance Costs	(652)	(715)
Subordinated Debt | 2029 Notes
Debt Instrument [Line Items]
Principal	37,000	37,000
Unamortized Debt Issuance Costs	(1,258)	(1,337)
Subordinated Debt | 2030 Notes
Debt Instrument [Line Items]
Principal	10,000	10,000
Unamortized Debt Issuance Costs	$ (219)	$ (231)