9.	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 and six month periods ended June 30, 2015 and 2014 (in thousands):


	For the Three Months				For the Six Months
	Ended June 30,				Ended June 30,
	2015		2014		2015		2014

Interest costs charged to expense	$	11,168	$	6,520	$	19,507	$	12,932
Amortization of deferred financing costs		1,105		861		1,889		1,697
Accretion of Convertible Notes		3,528		—		4,500		—

Interest expense		15,801		7,381		25,896		14,629
Interest costs capitalized to property and equipment		46		181		112		404
Interest costs capitalized to software		333		297		637		623

Total interest costs	$	16,180	$	7,859	$	26,645	$	15,656