Investments

Certificates of Deposit – We held approximately $6.0 million and $2.9 million in certificates of deposit at March 31, 2018 and December 31, 2017, respectively. At March 31, 2018, the certificates of deposit bear interest ranging from 1.00% to 1.60% per annum and have various maturities ranging from less than one month to approximately 4 months.

Investments Held to Maturity – Our investments held to maturity are comprised of $8.9 million of corporate notes and bonds with original maturities ranging from less than one month to approximately 4 months. The investments have moderate risk with S&P ratings ranging from AAA to BBB-.

We record the amortized cost basis and accrued interest of the corporate notes and bonds in the Consolidated Balance Sheets. We record the interest and amortization of bond premium to interest income in the Consolidated Statements of Income.

The following summarizes the amortized cost and estimated fair value of our investments held to maturity as of March 31, 2018 and December 31, 2017:



	Amortized Cost		Gross Unrealized Gain		Gross Unrealized (Loss)			Fair Value (Level 1)
March 31, 2018:	(in thousands)
Current assets:
Investments held to maturity	$	8,942	$	—	$	(11	)	$	8,931
Non current assets:
Investments held to maturity	—		—		—			—
Total	$	8,942	$	—	$	(11	)	$	8,931

December 31, 2017:
Current assets:
Investments held to maturity	$	6,077	$	—	$	(6	)	$	6,071
Non current assets:
Investments held to maturity	—		—		—			—
Total	$	6,077	$	—	$	(6	)	$	6,071