Consolidated Statement of Changes in Stockholders' Equity (Parenthetical) - USD ($) $ in Thousands		3 Months Ended		9 Months Ended
		Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Balance		$ 6,693,013	$ 6,674,678	$ 6,711,694	$ 6,655,235
Accounting Standards Update [Extensible List]				us-gaap:AccountingStandardsUpdate201613Member
Cumulative Effect, Period of Adoption, Adjustment
Balance	[1]			$ (10,468)
Accounting Standards Update [Extensible List]				us-gaap:AccountingStandardsUpdate201613Member
Common Stock (Par Value: $0.01)
Dividends paid on common stock, per share		$ 0.17	$ 0.17	$ 0.51	$ 0.51
Balance		$ 4,904	$ 4,904	$ 4,904	$ 4,904
Preferred Stock (Par Value: $0.01)
Dividends paid on preferred stock, per share		$ 15.94	$ 15.94	$ 47.82	$ 47.82
Balance		$ 502,840	$ 502,840	$ 502,840	$ 502,840
Retained Earnings
Balance		$ 362,724	$ 316,921	342,023	$ 297,202
Retained Earnings | Cumulative Effect, Period of Adoption, Adjustment
Balance	[1]			$ (10,468)
Accounting Standards Update [Extensible List]				us-gaap:AccountingStandardsUpdate201613Member

[1] Amount represents a $10.5 million cumulative adjustment, net of tax, to retained earnings as of January 1, 2020, as a result of the adoption of ASU 2016-13, Financial Instruments - Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments, which became effective January 1, 2020.