Securities Fair Value Option Securities (Details) - USD ($) $ in Thousands	Jun. 30, 2017	Dec. 31, 2016	Jun. 30, 2016
Schedule of Fair Value Option Securities [Line Items]
Fair Value Option Securities, Fair Value	$ 445,169	$ 77,046	$ 263,265
Fair Value Option Securities, Net Unrealized Gain or Loss	1,247	(1,777)	4,433
U.S. Treasury
Schedule of Fair Value Option Securities [Line Items]
Fair Value Option Securities, Fair Value	0	0	25,306
Fair Value Option Securities, Net Unrealized Gain or Loss	0	0	(43)
U.S. government agency residential mortgage-backed securities
Schedule of Fair Value Option Securities [Line Items]
Fair Value Option Securities, Fair Value	445,169	77,046	237,959
Fair Value Option Securities, Net Unrealized Gain or Loss	$ 1,247	$ (1,777)	$ 4,476