(4) Long-term Debt

Long-term debt is comprised of the following:

	As of December 31,
	2015			2016
	(In thousands)
10% Senior Secured Toggle Notes due 2020:
Principal	$	—		$	697,195
Discount, net of amortization		—			(11,955	)
7¾% Convertible Second Lien PIK Notes due 2019:
Principal		—			268,432
Accrued interest payable in kind		—			6,645
Discount, net of amortization		—			(61,230	)
9½% Convertible Second Lien PIK Notes due 2020:
Principal		—			174,182
Accrued interest payable in kind		—			735
Discount, net of amortization		—			(38,959	)
10% Senior Secured Notes due 2020:
Principal		700,000			2,805
7¾% Senior Notes due 2019:
Principal		376,090			17,959
Premium, net of amortization		3,583			118
9½% Senior Notes due 2020:
Principal		194,367			4,860
Discount, net of amortization		(5,040	)		(98	)
					0
Debt issuance costs, net of amortization		(19,670	)		(16,183	)
	$	1,249,330		$	1,044,506

The premium and discount on the senior notes are being amortized over the lives of the senior notes using the effective interest rate method. Issuance costs are amortized over the lives of the senior notes on a straight-line basis which approximates the amortization that would be calculated using an effective interest rate method.

The following table summarizes Comstock's principal amount of debt as of December 31, 2016 by year of maturity:

	2017		2018		2019		2020		2021		Thereafter		Total
	(In thousands)
10% Senior Secured Toggle Notes due 2020	$	—	$	—	$	—	$	697,195	$	—	$	—	$	697,195
7¾% Convertible Second Lien PIK Notes due 2019	$	—	$	—	$	268,432	$	—	$	—	$	—	$	268,432
9½% Convertible Second Lien PIK Notes due 2020		—		—		—		174,182		—		—		174,182
10% Senior Secured Notes due 2020		—		—		—		2,805		—		—		2,805
7¾% Senior Notes due 2019		—		—		17,959		—		—		—		17,959
9½% Senior Notes due 2020		—		—		—		4,860		—		—		4,860
	$	—	$	—	$	286,391	$	879,042	$	—	$	—	$	1,165,433

On September 6, 2016, Comstock completed a debt exchange with the holders of approximately 98% of its then outstanding senior notes. Specifically, the Company issued (i) $697.2 million of new 10% Senior Secured Toggle Notes due 2020 and warrants exercisable for 1,917,342 shares of common stock, in exchange for $697.2 million of the Company's 10% Senior Secured Notes due 2020, (ii) $270.6 million of new 7¾% Convertible Second Lien PIK Notes due 2019 in exchange for $270.6 million of the Company's 7¾% Senior Notes due 2019, and (iii) $169.7 million of new 9½% Convertible Second Lien PIK Notes due 2020 in exchange for $169.7 million of the Company's 9½% Senior Notes due 2020. Accrued and unpaid interest on notes tendered in the exchange was paid in cash. Following the exchange, $2.8 million of the 10% Senior Secured Notes, $18.0 million of the 7¾% Senior Notes and $4.9 million of the 9½% Senior Notes remained outstanding.

The exchange of the 10% Senior Secured Notes due 2020 for the 10% Senior Secured Toggle Notes due 2020 was accounted for as a modification of debt. Accordingly no gain or loss was recognized on the exchange. The value of the warrants issued to the noteholders on September 6, 2016, a Level 2 measurement, is being amortized to interest expense over the life of the notes. Transaction costs of $4.5 million related to the exchange were recognized in the year ended December 31, 2016 as a reduction to the gain on extinguishment of debt which is reported as a component of other income (loss). The exchange of the 7¾% Senior Notes due 2019 and the 9½% Senior Notes due 2020 for the Convertible Second Lien PIK Notes was accounted for as a debt extinguishment given the substantial difference in the terms of the exchanged notes. A gain of $106.2 million on extinguishment of debt was recognized on this exchange representing the difference between the fair market value of the new convertible notes and the carrying amount of the 7¾% Senior Notes due 2019 and the 9½% Senior Notes due 2020 that were exchanged. Transaction costs of $6.5 million related to these exchanges have been reflected as debt issuance costs which are being amortized to interest expense over the lives of the notes. The Company has determined the fair value of the convertible notes based upon the average trading prices for the notes subsequent to closing of the exchange. This valuation was a Level 2 measurement.

Interest on the 10% Senior Secured Toggle Notes is payable on March 15 and September 15, and the notes mature on March 15, 2020. The Company has the option to pay up to $75.0 million of accrued interest by issuing additional notes. To the extent that interest is paid in-kind, the interest rate increases to 12¼% only for that interest payment and would result in an additional $91.9 million of notes outstanding.

Interest on the 7¾% Convertible Second Lien PIK Notes is payable on April 1 and October 1, and these notes mature on April 1, 2019. Interest on the 9½% Convertible Second Lien PIK Notes is payable on June 15 and December 15, and these notes mature on June 15, 2020. Interest on the convertible notes is only payable in kind. Each series of the convertible notes is convertible, at the option of the holder, into 81.2 shares of the Company's common stock for each $1,000 of principal amount of notes. The convertible notes will mandatorily convert into 81.2 shares of common stock for each $1,000 of principal amount of the notes following a 15 consecutive trading day period during which the daily volume weighted average price of the Company's common stock is equal to or greater than $12.32 per share.

Prior to the completion of the debt exchange, the Company retired $87.5 million in principal amount of the 7¾% Senior Notes and $19.8 million of the 9½% Senior Notes in 2016 in exchange in the aggregate for the issuance of 2,748,403 shares of common stock and $3.5 million in cash. A gain on extinguishment of debt of $89.6 million was recognized on the retirement of the senior notes during 2016 for the difference between the market value of the stock and the net carrying value of the debt. During 2015, the Company acquired $23.9 million in principal amount of the 7¾% Senior Notes and $105.6 million in principal amount of the 9½% Senior Notes for an aggregate purchase price of $42.7 million. The gain of $82.4 million recognized on the purchase of the senior notes and the loss resulting from the write-off of deferred loan costs associated with the Company's prior bank credit facility of $3.7 million are included in the net gain on extinguishment of debt in 2015.

Comstock has a $50.0 million revolving credit facility with Bank of Montreal and Bank of America, N.A. that matures on March 4, 2019. As of December 31, 2016, there were no borrowings outstanding under the revolving credit facility. Indebtedness under the revolving credit facility is guaranteed by all of the Company's subsidiaries and is secured by substantially all of Comstock's and its subsidiaries' assets. Borrowings under the revolving credit facility bear interest, at Comstock's option, at either (1) LIBOR plus 2.5% or (2) the base rate (which is the higher of the administrative agent's prime rate, the federal funds rate plus 0.5% or 30 day LIBOR plus 1.0%) plus 1.5%. A commitment fee of 0.5% per annum is payable quarterly on the unused credit line. The revolving credit facility contains covenants that, among other things, restrict the payment of cash dividends and repurchases of common stock, limit the amount of additional debt that Comstock may incur and limit the Company's ability to make certain loans, investments and divestitures. The only financial covenants are the maintenance of a ratio of current assets, including availability under the revolving credit facility, to current liabilities of at least 1.0 to 1.0 and the maintenance of an asset coverage ratio of proved developed oil and natural gas reserves to the amount outstanding under the revolving credit facility of at least 2.5 to 1.0. The Company was in compliance with these covenants as of December 31, 2016.

All of the Company's subsidiaries guarantee the bank credit facility, the 10% Senior Secured Toggle Notes, the 7¾% Convertible Second Lien PIK Notes, the 9½% Convertible Second Lien PIK Notes, and the other outstanding senior notes. The bank credit facility, the 10% Senior Secured Toggle Notes and the convertible notes are secured by liens on substantially all of the Company's and its subsidiaries assets. The allocation of proceeds related to the liens on our assets are governed by intercreditor agreements granting priority to the bank credit facility. Proceeds from liens on the convertible notes are also subject to the priority of the 10% Senior Secured Toggle Notes. The liens that previously secured the 10% Senior Secured Notes that were not tendered for exchange were released and these notes are no longer secured.