Mortgage-Backed Securities and Agency CRT securities - Additional Information (Details) - USD ($)	9 Months Ended	12 Months Ended
	Sep. 30, 2013	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Schedule Of Available For Sale Securities [Line Items]
Impairment loss on mortgage-backed securities				$ 8,102,000
Minimum
Schedule Of Available For Sale Securities [Line Items]
Contractual maturity of Company's agency securities, in years		15 years
Maximum
Schedule Of Available For Sale Securities [Line Items]
Contractual maturity of Company's agency securities, in years		30 years
Agency Securities
Schedule Of Available For Sale Securities [Line Items]
Impairment loss on mortgage-backed securities	$ 8,102,000	$ 0	$ 0	$ 0