SECURITIES

The Company accounts for all of its securities, including RMBS, at estimated fair value. The following table summarizes the Company’s securities as of March 31, 2017 and December 31, 2016 (amounts in thousands):



	March 31, 2017						December 31, 2016
	Par		Amortized Cost		Estimated Fair Value		Par		Amortized Cost		Estimated Fair Value
Securities, at estimated fair value	$	337,428	$	261,274	$	271,477	$	371,785	$	304,628	$	229,206
Total	$	337,428	$	261,274	$	271,477	$	371,785	$	304,628	$	229,206

Net Realized and Unrealized Gains (Losses)

Realized gains or losses are measured by the difference between the net proceeds from the repayment or sale and the amortized cost basis of the asset without regard to unrealized gains or losses previously recognized. Unrealized gains or losses are computed as the difference between the estimated fair value of the asset and the amortized cost basis of such asset. Unrealized gains or losses primarily reflect the change in asset values, including the reversal of previously recorded unrealized gains or losses when gains or losses are realized. The following table presents the Company’s realized and unrealized gains (losses) from securities (amounts in thousands):



	Three months ended March 31, 2017		Three months ended March 31, 2016
Net realized gains (losses)	$	1,856	$	(1,593	)
Net (increase) decrease in unrealized losses	84,995		(50,126		)
Net realized and unrealized gains (losses)	$	86,851	$	(51,719	)

Defaulted Securities

As of both March 31, 2017 and December 31, 2016, the Company had no corporate debt securities in default.

Concentration Risk

The Company’s corporate debt securities portfolio has certain credit risk concentrated in a limited number of issuers. As of March 31, 2017, the Company’s corporate debt securities portfolio was concentrated in three issuers: Preferred Proppants LLC, LCI Helicopters Limited and Avoca Capital CLO XII Limited, which combined represented $213.9 million, or approximately 92% of the estimated fair value of the Company’s corporate debt securities. As of December 31, 2016, approximately 97% of the estimated fair value of the Company’s corporate debt securities portfolio was concentrated in ten issuers, with the three largest concentrations of debt securities in securities issued by LCI Helicopters Limited, Preferred Proppants LLC and Mizuho Bank Ltd., which combined represented $134.7 million, or approximately 71% of the estimated fair value of the Company’s corporate debt securities.

Pledged Assets

Note 6 to these condensed consolidated financial statements describes the Company’s borrowings under which the Company has pledged assets for borrowings. The following table summarizes the estimated fair value of securities pledged as collateral as of March 31, 2017 and December 31, 2016 (amounts in thousands):



	March 31, 2017		December 31, 2016
Pledged as collateral for collateralized loan obligation secured debt	$	2,158	$	13,337
Total	$	2,158	$	13,337