Consolidated Balance Sheets (Parenthetical) - USD ($) $ in Thousands	Dec. 31, 2017		Dec. 31, 2016
Stockholders' equity
Preferred stock, par value	$ 0.001		$ 0.001
Preferred stock, shares authorized	25,000,000		25,000,000
Preferred stock, shares issued	0		0
Preferred stock, shares outstanding	0		0
Common stock, par value	$ 0.001		$ 0.001
Common stock, shares authorized	600,000,000		600,000,000
Common stock, shares issued	402,549,346		402,334,655
Treasury stock, shares	457,041		3,906,877
Debt Instrument [Line Items]
Future interest payable - current	$ 105,188	[1]	$ 83,366
Future interest payable - long-term	2,979,086		2,909,732
Future interest payable on senior secured and convertible senior notes
Debt Instrument [Line Items]
Future interest payable - current	75,347		50,349
Future interest payable - long-term	$ 241,472		$ 178,476

[1] Future interest payable represents most of the interest due over the term of our 9% Senior Secured Second Lien Notes due 2021 (the “2021 Senior Secured Notes”), 9¼% Senior Secured Second Lien Notes due 2022 (the “2022 Senior Secured Notes”) and 3½% Convertible Senior Notes due 2024 (the “2024 Convertible Senior Notes”), which has been accounted for as debt in accordance with FASC 470-60, Troubled Debt Restructuring by Debtors. Our current maturities of long-term debt as of December 31, 2017 include $75.3 million of future interest payable related to these notes that is due within the next twelve months. See December 2017 and January 2018 Note Exchanges below for further discussion.