INVESTMENT SECURITIES

The following table presents the amortized cost and fair value of the investment securities portfolio as of the dates indicated:



($ in thousands)	Amortized Cost		Gross Unrealized Gains		Gross Unrealized Losses			Fair Value
March 31, 2018
Securities available-for-sale:
SBA loan pool securities	$	982	$	—	$	(12	)	$	970
U.S. government agency and U.S. government sponsored enterprise residential mortgage-backed securities	493,757		7		(26,265		)	467,499
Non-agency residential mortgage-backed securities	651		14		(1		)	664
Non-agency commercial mortgage-backed securities	201,613		334		(1,226		)	200,721
Collateralized loan obligations	1,743,941		10,899		(101		)	1,754,739
Total securities available-for-sale	$	2,440,944	$	11,254	$	(27,605	)	$	2,424,593
December 31, 2017
Securities available-for-sale:
SBA loan pool securities	$	1,056	$	2	$	—		$	1,058
U.S. government agency and U.S. government sponsored enterprise residential mortgage-backed securities	492,255		10		(15,336		)	476,929
Non-agency residential mortgage-backed securities	741		16		(1		)	756
Non-agency commercial mortgage-backed securities	305,172		5,339		—			310,511
Collateralized loan obligations	1,691,455		11,129		(266		)	1,702,318
Corporate debt securities	76,714		7,183		—			83,897
Total securities available-for-sale	$	2,567,393	$	23,679	$	(15,603	)	$	2,575,469

During the three months ended June 30, 2017, the Company evaluated its securities held-to-maturity and determined that certain securities no longer adhere to the Company’s strategic focus and could be sold or reinvested to potentially improve the Company’s liquidity position or duration profile. Accordingly, the Company was no longer able to assert that it had the intent to hold these securities until maturity. As a result, the Company transferred all $740.9 million of its securities held-to-maturity to securities available-for-sale, which resulted in a pre-tax increase to accumulated other comprehensive income of $22.0 million as of June 30, 2017. Due to the transfer, the Company’s ability to assert that it has the intent and ability to hold to maturity debt securities will be limited for the foreseeable future.

During the three months ended March 31, 2018, the Company completed the sale of all remaining corporate debt securities totaling $76.8 million to reposition its securities available-for-sale portfolio. At March 31, 2018, the Company's investment securities portfolio consisted of SBA loan pool securities, mortgage-backed securities, and collateralized loan obligations. The expected maturities of these types of securities may differ from contractual maturities because borrowers may have the right to call or prepay obligations with or without call or prepayment penalties.

At March 31, 2018 and December 31, 2017, there were no holdings of any one issuer, other than the U.S. Government and its agencies, in an amount greater than 10 percent of the Company's stockholders’ equity.

The following table presents proceeds from sales and calls of securities available-for-sale and the associated gross gains and losses realized through earnings upon the sales and calls of securities available-for-sale for the periods indicated:



	Three Months Ended March 31,
($ in thousands)	2018		2017
Gross realized gains on sales and calls of securities available-for-sale	$	5,241	$	3,356
Gross realized losses on sales and calls of securities available-for-sale	—		—
Net realized gains on sales and calls of securities available-for-sale	$	5,241	$	3,356
Proceeds from sales and calls of securities available-for-sale	$	287,517	$	378,539
Tax expense on sales and calls of securities available-for-sale	$	1,537	$	1,396

Investment securities with carrying values of $571.4 million and $564.4 million as of March 31, 2018 and December 31, 2017, respectively, were pledged to secure FHLB advances, public deposits, repurchase agreements, and for other purposes as required or permitted by law.

The following table summarizes the investment securities with unrealized losses by security type and length of time in a continuous unrealized loss position as of the dates indicated:



	Less Than 12 Months					12 Months or Longer					Total
($ in thousands)	Fair Value		Gross Unrealized Losses			Fair Value		Gross Unrealized Losses			Fair Value		Gross Unrealized Losses
March 31, 2018
Securities available-for-sale:
SBA loan pool securities	$	970	$	(12	)	$	—	$	—		$	970	$	(12	)
U.S. government agency and U.S. government sponsored enterprise residential mortgage-backed securities	$	13,570	$	(281	)	$	449,970	$	(25,984	)	$	463,540	$	(26,265	)
Non-agency residential mortgage-backed securities	—		—			118		(1		)	118		(1		)
Non-agency commercial mortgage-backed securities	144,673		(1,226		)	—		—			144,673		(1,226		)
Collateralized loan obligations	66,749		(101		)	—		—			66,749		(101		)
Total securities available-for-sale	$	225,962	$	(1,620	)	$	450,088	$	(25,985	)	$	676,050	$	(27,605	)
December 31, 2017
Securities available-for-sale:
U.S. government agency and U.S. government sponsored enterprise residential mortgage-backed securities	$	4,880	$	(35	)	$	470,092	$	(15,301	)	$	474,972	$	(15,336	)
Non-agency residential mortgage-backed securities	—		—			148		(1		)	148		(1		)
Collateralized loan obligations	104,334		(266		)	—		—			104,334		(266		)
Total securities available-for-sale	$	109,214	$	(301	)	$	470,240	$	(15,302	)	$	579,454	$	(15,603	)

The Company did not record OTTI for investment securities for the three months ended March 31, 2018 or 2017.

At March 31, 2018, the Company’s securities available-for-sale portfolio consisted of 177 securities, 56 of which were in an unrealized loss position. At December 31, 2017, the Company’s securities available-for-sale portfolio consisted of 191 securities, 33 of which were in an unrealized loss position.

The Company monitors its securities portfolio to ensure it has adequate credit support. As of March 31, 2018, the Company believed there was no OTTI and did not have the intent to sell its securities in an unrealized loss position and it is not likely that it will be required to sell these securities before their anticipated recovery. The Company considers the lowest credit rating for identification of potential OTTI. As of March 31, 2018, all of the Company's investment securities in an unrealized loss position received an investment grade credit rating.