Investments - Additional Information (Details) $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2020 USD ($) security numberOfInvestments	Dec. 31, 2019 USD ($) security
Investment Holdings [Line Items]
Vertical risk retention interest	5.00%
Trading investments	$ 11,360	$ 0
Available-for-sale investments, cost	$ 607,867	485,756
Number of securities in net loss position | numberOfInvestments	10
Par value of mortgage-backed securities pledged to FRB	$ 285,000	252,000
Gain on equity securities investment	8,000
Non-marketable securities investment	26,000	26,000
Low income housing tax credit investments	57,000	58,000
Low income housing tax credit investments, liability for unfunded commitments	25,000	29,000
Low income housing tax credit investments, tax credits and benefits	$ 1,000	$ 6,000
Low income housing tax credit investments, expected tax benefits recognized	25.00%
Student Loan
Investment Holdings [Line Items]
Private education loans sold	$ 1,700,000
Mortgage-backed securities
Investment Holdings [Line Items]
Number of securities in net loss position | security	0	33
Number of mortgage-backed securities | security		107
Utah Housing Corporation bonds
Investment Holdings [Line Items]
Number of securities in net loss position | security	1
Number of mortgage-backed securities | security	3
U.S. government-sponsored enterprises
Investment Holdings [Line Items]
Number of securities in net loss position | security	1
Number of government sponsored securities | security	20
Ginnie Mae | Mortgage-backed securities
Investment Holdings [Line Items]
Available-for-sale investments, cost	$ 51,000
Number of securities in net loss position | security		18
Number of mortgage-backed securities | security		33
Fannie Mae | Mortgage-backed securities
Investment Holdings [Line Items]
Available-for-sale investments, cost	104,000
Freddie Mac | Mortgage-backed securities
Investment Holdings [Line Items]
Available-for-sale investments, cost	$ 52,000