Investments

The following table presents (losses) gains due to changes in fair value of investments that are measured at fair value pursuant to application of the fair value option:



	Year Ended December 31,
	2015			2014			2013
	(Amounts in thousands)
Fixed maturity securities	$	(39,304	)	$	77,208		$	(100,703	)
Equity securities	(22,988		)	(32,922		)	56,822
Short-term investments	561			(527		)	(156		)
Total	$	(61,731	)	$	43,759		$	(44,037	)

The following table presents gross gains (losses) realized on the sales of investments:



	Year Ended December 31,
	2015								2014								2013
	(Amounts in thousands)
	Gross Realized Gains		Gross Realized Losses			Net			Gross Realized Gains		Gross Realized Losses			Net			Gross Realized Gains		Gross Realized Losses			Net
Fixed maturity securities	$	631	$	(495	)	$	136		$	7,015	$	(9,734	)	$	(2,719	)	$	9,320	$	(3,842	)	$	5,478
Equity securities	41,305		(58,764		)	(17,459		)	59,342		(17,705		)	41,637			82,385		(58,297		)	24,088
Short-term investments	—		(1,396		)	(1,396		)	—		(1,943		)	(1,943		)	—		(903		)	(903		)

Contractual Maturity

At December 31, 2015, fixed maturity holdings rated below investment grade and non-rated comprised 1.3% of total investments at fair value. Additionally, the Company owns securities that are credit enhanced by financial guarantors that are subject to uncertainty related to market perception of the guarantors’ ability to perform. Determining the estimated fair value of municipal bonds could become more difficult should markets for these securities become illiquid.

The following table presents the estimated fair values of the Company's fixed maturity securities at December 31, 2015 by contractual maturity. Expected maturities will differ from contractual maturities because borrowers may have the right to call or prepay obligations with or without call or prepayment penalties.



	Estimated Fair Value
	(Amounts in thousands)
Fixed maturity securities:
Due in one year or less	$	108,775
Due after one year through five years	394,240
Due after five years through ten years	609,243
Due after ten years	1,767,745
Total	$	2,880,003

Investment Income

The following table presents a summary of net investment income:



	Year Ended December 31,
	2015			2014			2013
	(Amounts in thousands)
Fixed maturity securities	$	108,122		$	104,946		$	107,926
Equity securities	14,630			17,313			18,249
Short-term investments	9,033			8,561			2,702
Total investment income	$	131,785		$	130,820		$	128,877
Less: investment expense	(5,486		)	(5,097		)	(4,339		)
Net investment income	$	126,299		$	125,723		$	124,538