4. Investments

Investments consisted principally of commercial paper and corporate bond securities and are classified as available-for-sale as of December 31, 2017 and September 30, 2017. Available-for-sale securities are reported at fair value with unrealized gains and losses, net of tax, excluded from the condensed consolidated statements of operations and reported in the condensed consolidated statements of comprehensive (loss) income as well as a separate component of stockholders’ equity in the condensed consolidated balance sheets, except for other-than-temporary impairments, which are reported as a charge to current earnings. A loss would be recognized when there is an other-than-temporary impairment in the fair value of any individual security classified as available-for-sale, with the associated net unrealized loss reclassified out of accumulated other comprehensive income with a corresponding adjustment to other income (loss). This adjustment results in a new cost basis for the investment. Interest earned on debt securities, including amortization of premiums and accretion of discounts, is included in other income. Realized gains and losses from the sales of debt securities, which are included in other income, are determined using the specific identification method. Investment purchases are accounted for on the date the trade is executed, which may not be the same as the date the transaction is cash settled.

The amortized cost, unrealized holding gains and losses, and fair value of available-for-sale securities were as follows:

	December 31, 2017
(Dollars in thousands)	Amortized Cost		Unrealized Gains		Unrealized Losses			Fair Value
Commercial paper and corporate bonds	$	24,782	$	—	$	(26	)	$	24,756
Total	$	24,782	$	—	$	(26	)	$	24,756

	September 30, 2017
(Dollars in thousands)	Amortized Cost		Unrealized Gains		Unrealized Losses			Fair Value
Commercial paper and corporate bonds	$	31,817	$	—	$	(15	)	$	31,802
Total	$	31,817	$	—	$	(15	)	$	31,802