Fair Value of Financial Instruments - Hierarchy Table on Recurring Basis (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Financial assets
Investment securities available-for-sale, at fair value	$ 3,600,731	$ 1,368,384
U.S. Treasury
Financial assets
Investment securities available-for-sale, at fair value	32,739	63,555
Agency
Financial assets
Investment securities available-for-sale, at fair value	603,045	246,358
Corporate
Financial assets
Investment securities available-for-sale, at fair value	397,536	151,353
Municipal bonds
Financial assets
Investment securities available-for-sale, at fair value	1,313,908	397,298
Collateralized mortgage obligations
Financial assets
Investment securities available-for-sale, at fair value	358,280	9,984
Mortgage-backed securities
Financial assets
Investment securities available-for-sale, at fair value	895,223	499,836
Level 1
Financial assets
Investment securities available-for-sale, at fair value	0	0
Derivative assets	0	0
Financial liabilities
Derivative liabilities	0	0
Level 2
Financial assets
Investment securities available-for-sale, at fair value	3,600,731	1,368,384
Derivative assets	14,697	2,103
Financial liabilities
Derivative liabilities	14,789	2,103
Level 3
Financial assets
Investment securities available-for-sale, at fair value	0	0
Derivative assets	1,920	0
Financial liabilities
Derivative liabilities	0	0
Recurring
Financial assets
Investment securities available-for-sale, at fair value	3,600,731	1,368,384
Derivative assets	16,617	2,103
Financial liabilities
Derivative liabilities	14,789	2,103
Recurring | Interest rate swaps
Financial assets
Derivative assets	14,697
Recurring | Equity warrants
Financial assets
Derivative assets	1,920
Recurring | U.S. Treasury
Financial assets
Investment securities available-for-sale, at fair value	32,739	63,555
Recurring | Agency
Financial assets
Investment securities available-for-sale, at fair value	603,045	246,358
Recurring | Corporate
Financial assets
Investment securities available-for-sale, at fair value	397,536	151,353
Recurring | Municipal bonds
Financial assets
Investment securities available-for-sale, at fair value	1,313,908	397,298
Recurring | Collateralized mortgage obligations
Financial assets
Investment securities available-for-sale, at fair value	358,280	9,984
Recurring | Mortgage-backed securities
Financial assets
Investment securities available-for-sale, at fair value	895,223	499,836
Recurring | Level 1
Financial assets
Investment securities available-for-sale, at fair value	0	0
Derivative assets	0	0
Financial liabilities
Derivative liabilities	0	0
Recurring | Level 1 | Interest rate swaps
Financial assets
Derivative assets	0
Recurring | Level 1 | Equity warrants
Financial assets
Derivative assets	0
Recurring | Level 1 | U.S. Treasury
Financial assets
Investment securities available-for-sale, at fair value	0	0
Recurring | Level 1 | Agency
Financial assets
Investment securities available-for-sale, at fair value	0	0
Recurring | Level 1 | Corporate
Financial assets
Investment securities available-for-sale, at fair value	0	0
Recurring | Level 1 | Municipal bonds
Financial assets
Investment securities available-for-sale, at fair value	0	0
Recurring | Level 1 | Collateralized mortgage obligations
Financial assets
Investment securities available-for-sale, at fair value	0	0
Recurring | Level 1 | Mortgage-backed securities
Financial assets
Investment securities available-for-sale, at fair value	0	0
Recurring | Level 2
Financial assets
Investment securities available-for-sale, at fair value	3,600,731	1,368,384
Derivative assets	14,697	2,103
Financial liabilities
Derivative liabilities	14,789	2,103
Recurring | Level 2 | Interest rate swaps
Financial assets
Derivative assets	14,697
Recurring | Level 2 | Equity warrants
Financial assets
Derivative assets	0
Recurring | Level 2 | U.S. Treasury
Financial assets
Investment securities available-for-sale, at fair value	32,739	63,555
Recurring | Level 2 | Agency
Financial assets
Investment securities available-for-sale, at fair value	603,045	246,358
Recurring | Level 2 | Corporate
Financial assets
Investment securities available-for-sale, at fair value	397,536	151,353
Recurring | Level 2 | Municipal bonds
Financial assets
Investment securities available-for-sale, at fair value	1,313,908	397,298
Recurring | Level 2 | Collateralized mortgage obligations
Financial assets
Investment securities available-for-sale, at fair value	358,280	9,984
Recurring | Level 2 | Mortgage-backed securities
Financial assets
Investment securities available-for-sale, at fair value	895,223	499,836
Recurring | Level 3
Financial assets
Investment securities available-for-sale, at fair value	0	0
Derivative assets	1,920	0
Financial liabilities
Derivative liabilities	0	0
Recurring | Level 3 | Interest rate swaps
Financial assets
Derivative assets	0
Recurring | Level 3 | Equity warrants
Financial assets
Derivative assets	1,920
Recurring | Level 3 | U.S. Treasury
Financial assets
Investment securities available-for-sale, at fair value	0	0
Recurring | Level 3 | Agency
Financial assets
Investment securities available-for-sale, at fair value	0	0
Recurring | Level 3 | Corporate
Financial assets
Investment securities available-for-sale, at fair value	0	0
Recurring | Level 3 | Municipal bonds
Financial assets
Investment securities available-for-sale, at fair value	0	0
Recurring | Level 3 | Collateralized mortgage obligations
Financial assets
Investment securities available-for-sale, at fair value	0	0
Recurring | Level 3 | Mortgage-backed securities
Financial assets
Investment securities available-for-sale, at fair value	$ 0	$ 0