Investments

We invest in pre-funded municipal bonds, which are generally secured by escrowed-to-maturity U.S. Treasury notes. Municipal bonds represent debt obligations issued by states, cities, counties and other governmental entities, which earn interest that is exempt from federal income taxes. Additionally, we invest in certificates of deposit issued by financial institutions and corporate bonds from large cap industrial and selected financial companies with a minimum credit rating of A. We have the ability and intention to hold our investments until maturity and therefore classify these investments as held-to-maturity and report them at amortized cost.

Amortized cost and fair value for investments classified as held-to-maturity at March 31, 2016 were as follows:



								Estimated
	Amortized		Gross Unrealized					Fair Market
	Cost		Gains		Losses			Value
Due in less than 1 year:
Municipal bonds	$	4,851	$	2	$	—		$	4,853
Corporate bonds	3,960		1		(1		)	3,960
Certificates of deposit	1,291		—		—			1,291
Due in 1 - 2 years:
Municipal bonds	47		—		—			47
	$	10,149	$	3	$	(1	)	$	10,151

Amortized cost and fair value for investments classified as held-to-maturity at September 30, 2015 were as follows:



								Estimated
	Amortized		Gross Unrealized					Fair Market
	Cost		Gains		Losses			Value
Due in less than 1 year:
Municipal bonds	$	13,117	$	14	$	(1	)	$	13,130
Corporate bonds	11,402		1		(10		)	11,393
Certificates of deposit	3,567		—		—			3,567
Due in 1 - 2 years:
Municipal bonds	771		2		—			773
Corporate bonds	201		—		—			201
Certificates of deposit	747		—		—			747
	$	29,805	$	17	$	(11	)	$	29,811

Investments are exposed to various risks, including interest rate, market and credit risk, and as a result, it is possible that changes in the values of these investments may occur and that such changes could affect the amounts reported in the condensed consolidated balance sheets and condensed consolidated statements of comprehensive income (loss).