Mortgage-Backed Securities - Additional Information (Details) (USD $) In Thousands, unless otherwise specified	3 Months Ended	12 Months Ended		9 Months Ended
	Sep. 30, 2013	Dec. 31, 2013	Dec. 31, 2014	Sep. 30, 2013
Schedule Of Available For Sale Securities [Line Items]
Impairment loss on mortgage-backed securities	$ 8,102	$ 8,102
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			0	$ 8,102