10.

Interest Costs

We capitalize a portion of our interest on funds borrowed during the active construction period of major capital projects. Capitalized interest is added to the cost of the underlying assets and amortized over the useful lives of the assets.

The following is a summary of our interest costs for the three month periods ended March 31, 2018 and 2017 (in thousands):


	For the Three Months
	Ended March 31,
	2018			2017
Interest costs charged to expense	$	24,980		$	21,539
Amortization of deferred financing costs		1,035			896
Accretion of debt discount on Convertible Notes		5,224			4,681
Amortization of debt premium on Senior Secured Notes		(685	)		(173	)

Interest expense		30,554			26,943
Interest costs capitalized to property and equipment		12			4
Interest costs capitalized to software		32			358

Total interest costs	$	30,598		$	27,305