Securities Fair Value Option Securities (Details) - USD ($) $ in Thousands	Sep. 30, 2020	Dec. 31, 2019
Fair Value Option Securities [Line Items]
Fair value option securities, Fair Value	$ 134,756	$ 1,098,577
Fair value option securities, Net Unrealized Gain (Loss)	4,926	14,061
U.S. Treasury [Member]
Fair Value Option Securities [Line Items]
Fair value option securities, Fair Value	0	9,917
Fair value option securities, Net Unrealized Gain (Loss)	0	(48)
Residential agency mortgage-backed securities [Member]
Fair Value Option Securities [Line Items]
Fair value option securities, Fair Value	134,756	1,088,660
Fair value option securities, Net Unrealized Gain (Loss)	$ 4,926	$ 14,109