CONDENSED CONSOLIDATED STATEMENT OF STOCKHOLDERS' EQUITY - USD ($) $ in Thousands		Total	Common Stock	Additional Paid-In Capital	Retained Earnings (Accumulated Deficit)	Accumulated Other Comprehensive Income (Loss)	Non- controlling Interest
Balance at beginning of period (shares) at Dec. 31, 2017			91,123,759
Balance at beginning of period at Dec. 31, 2017		$ 655,947	$ 911	$ 659,227	$ 74,219	$ (78,410)	$ 0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock (shares)			246,180
Issuance of common stock		42	$ 2	40
Repurchase of shares for withholding taxes (shares)			(37,612)
Repurchase of shares for withholding taxes		(365)		(365)
Share-based compensation expense		1,742		1,742
Net income (loss)		(265)			(265)
Dividends		(8,365)			(8,365)
Reclassification of stranded tax effects related to the Tax Act	[1]				16,847	(16,847)
Other comprehensive income:
Pension and other postretirement benefit liability adjustment, net of tax		1,624				1,624
Balance at end of period (shares) at Mar. 31, 2018			91,332,327
Balance at end of period at Mar. 31, 2018		650,360	$ 913	660,644	82,436	(93,633)	0
Balance at beginning of period (shares) at Dec. 31, 2017			91,123,759
Balance at beginning of period at Dec. 31, 2017		655,947	$ 911	659,227	74,219	(78,410)	0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Repurchase of shares for withholding taxes (shares)			0
Net income (loss)		(40,359)
Net loss attributable to non-controlling interest		0
Reclassification of stranded tax effects related to the Tax Act						(16,847)
Other comprehensive income:
Pension and other postretirement benefit liability adjustment, net of tax		3,226
Balance at end of period (shares) at Jun. 30, 2018			91,368,529
Balance at end of period at Jun. 30, 2018		617,461	$ 914	662,883	33,943	(92,031)	11,752
Balance at beginning of period (shares) at Mar. 31, 2018			91,332,327
Balance at beginning of period at Mar. 31, 2018		650,360	$ 913	660,644	82,436	(93,633)	0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock (shares)			41,628
Issuance of common stock		$ 338	$ 1	337
Repurchase of shares for withholding taxes (shares)		0	(5,426)
Repurchase of shares for withholding taxes		$ (48)		(48)
Share-based compensation expense		1,950		1,950
Net income (loss)		(40,094)			(40,094)
Fair value of non-controlling interest acquired		11,752
Net loss attributable to non-controlling interest		0
Dividends		(8,399)			(8,399)
Other comprehensive income:
Pension and other postretirement benefit liability adjustment, net of tax		1,602				1,602
Balance at end of period (shares) at Jun. 30, 2018			91,368,529
Balance at end of period at Jun. 30, 2018		$ 617,461	$ 914	662,883	33,943	(92,031)	11,752
Balance at beginning of period (shares) at Dec. 31, 2018		91,438,768	91,438,768
Balance at beginning of period at Dec. 31, 2018		$ 314,732	$ 914	661,630	(260,977)	(98,607)	11,772
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock (shares)			390,640
Issuance of common stock		163	$ 4	159
Repurchase of shares for withholding taxes (shares)			(90,937)
Repurchase of shares for withholding taxes		(376)	$ (1)	(375)
Share-based compensation expense		1,293		1,293
Net income (loss)		(61,574)			(61,574)
Net loss attributable to non-controlling interest		(253)					(253)
Repurchase of subsidiary's common stock		(28)					(28)
Dividends	[2]	61			61
Other comprehensive income:
Pension and other postretirement benefit liability adjustment, net of tax		2,128				2,128
Balance at end of period (shares) at Mar. 31, 2019			91,738,471
Balance at end of period at Mar. 31, 2019		$ 256,146	$ 917	662,707	(322,490)	(96,479)	11,491
Balance at beginning of period (shares) at Dec. 31, 2018		91,438,768	91,438,768
Balance at beginning of period at Dec. 31, 2018		$ 314,732	$ 914	661,630	(260,977)	(98,607)	11,772
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Repurchase of shares for withholding taxes (shares)			0
Net income (loss)		(126,045)
Net loss attributable to non-controlling interest		(645)
Other comprehensive income:
Pension and other postretirement benefit liability adjustment, net of tax		$ 4,548
Balance at end of period (shares) at Jun. 30, 2019		91,884,320	91,884,320
Balance at end of period at Jun. 30, 2019		$ 195,759	$ 919	664,732	(386,932)	(94,059)	11,099
Balance at beginning of period (shares) at Mar. 31, 2019			91,738,471
Balance at beginning of period at Mar. 31, 2019		256,146	$ 917	662,707	(322,490)	(96,479)	11,491
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock (shares)			163,826
Issuance of common stock		$ 211	$ 2	209
Repurchase of shares for withholding taxes (shares)		0	(17,977)
Repurchase of shares for withholding taxes		$ (31)		(31)
Share-based compensation expense		1,847		1,847
Net income (loss)		(64,471)			(64,471)
Net loss attributable to non-controlling interest		(392)					(392)
Dividends	[2]	29			29
Other comprehensive income:
Pension and other postretirement benefit liability adjustment, net of tax		$ 2,420				2,420
Balance at end of period (shares) at Jun. 30, 2019		91,884,320	91,884,320
Balance at end of period at Jun. 30, 2019		$ 195,759	$ 919	$ 664,732	$ (386,932)	$ (94,059)	$ 11,099

[1] Refer to Note 1 - Recently Adopted Accounting Pronouncements within our Notes to unaudited Condensed Consolidated Financial Statements for additional details on the adoption of ASU No. 2018-02 during the first quarter of 2018.

[2] During the three months ended March 31, 2019 and the three months ended June 30, 2019, participants forfeited accrued dividends related to previously-granted restricted share units ("RSUs") and performance share units ("PSUs"), causing a reduction to our accumulated deficit position. Under our long-term incentive compensation program, cash dividend equivalent units for RSUs and PSUs are accrued over time as our Board of Directors declares cash dividends and vest in cash at the same time as the underlying award. No dividends were declared or paid during the three months ended March 31, 2019 and three months ended June 30, 2019.