Fair Value Measurements - Nonrecurring Basis (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020	Dec. 31, 2020
Fair value measurements at reporting date using:
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets: Impaired loans	$ 7,035,003		$ 6,980,202
Fair value measurements at reporting date using: | Quoted prices in active markets for identical assets (Level 1)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets: Impaired loans	0		0
Fair value measurements at reporting date using: | Significant  other observable inputs (Level 2)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets: Impaired loans	0		0
Fair value measurements at reporting date using: | Significant unobservable inputs (Level 3)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets: Impaired loans	7,035,003		$ 6,980,202
Fair value measurements at reporting date using: | Fair Value, Measurements, Nonrecurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets: Impaired loans	5,205	$ 97
Fair value measurements at reporting date using: | Fair Value, Measurements, Nonrecurring | Quoted prices in active markets for identical assets (Level 1)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets: Impaired loans	0	0
Fair value measurements at reporting date using: | Fair Value, Measurements, Nonrecurring | Significant  other observable inputs (Level 2)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets: Impaired loans	0	0
Fair value measurements at reporting date using: | Fair Value, Measurements, Nonrecurring | Significant unobservable inputs (Level 3)
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Assets: Impaired loans	5,205	97
Gain (losses) from fair value changes | Fair Value, Measurements, Nonrecurring
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Gain (losses) from fair value changes	$ (435)	$ 21