Recent Accounting Pronouncements (Details) - USD ($)	Dec. 31, 2020	Jan. 01, 2020	Dec. 31, 2019		Jan. 01, 2019	Dec. 31, 2018		Dec. 31, 2017
New Accounting Pronouncements or Change in Accounting Principle [ Line Items ]
Allowance for credit losses	$ 247,042,000	$ 76,000,000.0	$ 109,222,000			$ 103,419,000		$ 96,729,000
Debt securities, held-to-maturity, allowance for credit loss	(220,000)	220,000
Stockholders' equity	(2,690,006,000)		(2,370,793,000)			(2,054,998,000)		(1,864,874,000)
Subordinated debt	234,768,000		233,948,000
Debt Modified Under C A R E S Act
New Accounting Pronouncements or Change in Accounting Principle [ Line Items ]
Subordinated debt	96,700,000
Cumulative Effect, Period of Adoption, Adjustment
New Accounting Pronouncements or Change in Accounting Principle [ Line Items ]
Allowance for credit losses			75,757,000
Stockholders' equity			26,821,000	[1]		(47,257,000)	[2]	0
Unfunded loan commitment
New Accounting Pronouncements or Change in Accounting Principle [ Line Items ]
Allowance for credit losses		5,600,000
PCD
New Accounting Pronouncements or Change in Accounting Principle [ Line Items ]
Allowance for credit losses	31,127,000	35,700,000	3,197,000
Non-PCD
New Accounting Pronouncements or Change in Accounting Principle [ Line Items ]
Allowance for credit losses		8,500,000
Retained Earnings
New Accounting Pronouncements or Change in Accounting Principle [ Line Items ]
Stockholders' equity	$ (1,388,525,000)		(1,380,612,000)			(1,192,767,000)		(1,074,990,000)
Retained Earnings | Cumulative Effect, Period of Adoption, Adjustment
New Accounting Pronouncements or Change in Accounting Principle [ Line Items ]
Stockholders' equity			$ 26,821,000	[1]	$ (47,300,000)	$ (47,257,000)	[2]	$ (6,689,000)	[3]
Loans
New Accounting Pronouncements or Change in Accounting Principle [ Line Items ]
Allowance for credit losses		$ 26,000,000.0

[1] As a result of accounting guidance adopted in the first quarter of 2020, a portion of the increase in allowance for credit losses, net of tax, was recognized as a cumulative-effect adjustment to retained earnings as of January 1, 2020. For further discussion of this guidance, see Note 2, "Recent Accounting Pronouncements."

[2] As a result of accounting guidance adopted in 2019, the remaining deferred gain on a sale-leaseback transaction was recognized as a cumulative-effect adjustment to retained earnings as of January 1, 2019.

[3] As a result of accounting guidance adopted in 2018, certain reclassifications were made from accumulated other comprehensive loss to retained earnings as of January 1, 2018.