Interest expense

6 Months Ended

12 Months Ended

Jun. 30, 2018

Dec. 31, 2017

Interest and Debt Expense [Abstract]

Interest Expense

(8)   Interest expense

The following tables present the components of interest expense:

	For the six months ended June 30,
	2018		2017
(Dollars in thousands)
Interest incurred on debt	$	35,473	$	12,086
Related party Promissory Note interest expense		5,090		—
Senior Note redemption premium		4,782		—
Accretion of fair value adjustment on Senior Notes		19,414		3,208
Accretion of original issue discount on 2018 Term Loans		357		—
Amortization of debt issuance costs		1,416		154
Total interest expense	$	66,532	$	15,448

Interest rates

The 2018 Credit Agreement had an effective interest rate of 5.59% as of June 30, 2018. The Old Revolving Facility and Old Term Loan Facility had an effective interest rate of 4.57% as of December 31, 2017 and the Senior Notes had a fixed interest rate of 6.375%, both of which were repaid on February 12, 2018 as part of our refinancing (see Note 6 "Debt and liquidity").

As a result of our February 12, 2018 refinancing, we paid a prepayment premium for the redemption of our Senior Notes totaling $4.8 million. The accretion of the August 15, 2015 fair value adjustment to our Senior Notes totaling $19.4 million included accelerated accretion of $18.7 million for the six months ended June 30, 2018 resulting from the prepayment.

(8)   Interest expense

The following table presents an analysis of interest expense:

	Successor						Predecessor
	For the year ended December 31, 2017		For the year ended December 31, 2016		For the period August 15 through December 31, 2015		For the period January 1 through August 14, 2015
	(Dollars in thousands)
Interest incurred on debt	$	24,060	$	20,408	$	7,694	$	12,066
Amortization of discount on Senior Subordinated Notes	—		—		—		12,027
Accretion of fair value adjustment on Senior Notes	6,454		6,305		2,305		—
Amortization of debt issuance costs	309		201		—		2,118
Total interest expense	$	30,823	$	26,914	$	9,999	$	26,211

Interest rates

The revolving facility had an effective interest rate of 4.57% and 5.52% as of December 31, 2017 and 2016, respectively. The Senior Notes carried an interest rate of 6.375%. The Senior Subordinated Notes had an implied rate of 7.00%.

On August 11, 2015, we prepaid our Senior Subordinated Notes (see Note 7 "Debt and liquidity"). This prepayment resulted in accelerated amortization of $4.5 million as the Senior Subordinated Notes were prepaid at the face value. The accelerated expense was recorded in the predecessor period.