Stockholders' Equity (Amounts Reclassified out of AOCI) (Details) - USD ($) $ in Thousands	3 Months Ended	6 Months Ended
Jun. 30, 2019	Jun. 30, 2018	Jun. 30, 2019	Jun. 30, 2018	Dec. 31, 2018
Amounts Reclassified from AOCI
Realized gain on sale of securities	$ 7,710	$ 7,429	$ 32,319	$ 16,246
Net Income Available to Common Stock and Participating Securities	89,014	66,404	173,865	145,830
Total reclassifications for period	(7,114)	(5,178)	(22,660)	(15,458)
Accumulated Other Comprehensive Income/(Loss)
Unrealized losses recorded in AOCI on securities for which Other-than-temporary impairments had been recognized in earnings in prior periods	0		0		$ 224
Amounts Reclassified from AOCI \| Accumulated Net Investment Gain (Loss) Including Portion Attributable to Noncontrolling Interest
Amounts Reclassified from AOCI
Realized gain on sale of securities	(6,371)	(5,178)	(21,576)	(15,458)
Net Income Available to Common Stock and Participating Securities	(6,371)	$ (5,178)	(21,576)	$ (15,458)
Total Swaps designated as cash flow hedges	$ (743)		$ (1,084)

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Amount of realized gain (loss) on investment in debt security measured at fair value with change in fair value recognized in other comprehensive income (available-for-sale), investment in debt security measured at amortized cost (held-to-maturity) and investment in debt security measured at fair value with change in fair value recognized in net income (trading). Excludes other-than-temporary impairment (OTTI).

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Amount, after deduction of tax, noncontrolling interests, dividends on preferred stock and participating securities; of income (loss) available to common shareholders.

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