Fair Value - Carrying Value of CDOs (Details) $ in Thousands		3 Months Ended			9 Months Ended
		Sep. 30, 2017 USD ($) security	Mar. 31, 2017 USD ($)	Sep. 30, 2016 USD ($)	Sep. 30, 2017 USD ($)	Sep. 30, 2016 USD ($)
Rollforward of the Carrying Value of CDOs [Roll Forward]
Carrying Value of CDOs sold			$ 210,200
CDOs
Rollforward of the Carrying Value of CDOs [Roll Forward]
Beginning balance		$ 33,454	$ 33,260	$ 30,431	$ 33,260	$ 31,529
Change in other comprehensive income	[1]	(739)		1,794	(604)	764
Other		(1,889)		(326)	(1,830)	(394)
Ending balance		$ 30,826		$ 31,899	$ 30,826	$ 31,899
Number Of Securities Sold | security		3
Carrying Value of CDOs sold		$ 1,900

[1] Included in unrealized holding gains in the Consolidated Statements of Comprehensive Income.