Other Assets - Derivative Instruments (Details 3) - USD ($) $ in Thousands		3 Months Ended		9 Months Ended		12 Months Ended
	Dec. 31, 2014	Sep. 30, 2016	Sep. 30, 2015	Sep. 30, 2016	Sep. 30, 2015	Dec. 31, 2015
Other Assets [Abstract]
MBS securities recorded upon adoption of revised accounting standard						$ 1,900,000
CRT securities recorded upon adoption of revised accounting standard						4,600
Repurchase agreements recorded upon adoption of revised accounting standard for repurchase agreement financing				$ 0	$ 1,519,593	$ 1,500,000
Cumulative effect adjustment on adoption of revised accounting standard for repurchase agreement financing	$ 4,500	$ 0	$ 0	$ 0	$ 4,537