Debtor in Possession - Condensed Balance Sheet (Details) - USD ($) $ / shares in Units, $ in Thousands	Mar. 31, 2019	Dec. 31, 2018	Mar. 31, 2018	Dec. 31, 2017
Condensed Balance Sheet Statements, Captions [Line Items]
Cash and cash equivalents	$ 15,884	$ 50,874	$ 7,431	$ 8,770
Short-term investments	73,336	14,232
Trade	167,561	168,459
Other	11,252	14,006
Inventories of spare parts – net	52,988	56,698
Prepaid expenses	13,944	11,419
Income taxes receivable	942	950
Total current assets	335,907	316,638
Property and equipment – net	896,436	902,485
Right of use assets	144,198
Restricted cash and investments	19,789	19,781
Other assets	18,981	18,378
Total assets	1,419,832	1,262,226
Accounts payable	38,854	50,289
Accrued and other current liabilities	31,208	45,292
Accrued and other current liabilities	26,544
Current maturities of long term debt	875	500,000
Total current liabilities	97,481	595,321
Term loan issued March 13, 2019, net of debt issuance costs of $5,609	63,516	0
Related party term loan issued September 28, 2018, net of debt issuance costs of $656 and $765, respectively	129,344	129,235
Deferred income taxes	55,098	59,178
Other long-term liabilities	3,324	5,059
Long-term operating lease liabilities	118,436
Total liabilities not subject to compromise	467,199	788,793
Liabilities subject to compromise	513,125
Total liabilities	980,324	788,793
Additional paid-in capital	314,818	314,316
Accumulated other comprehensive income (loss)	(3,138)	(3,952)
Retained earnings	126,246	161,487
Total shareholders’ equity	439,508	473,433	597,735	612,654
Total liabilities and shareholders’ equity	1,419,832	1,262,226
Voting Common Stock [Member]
Condensed Balance Sheet Statements, Captions [Line Items]
Common stock	$ 291	$ 291
Common stock, par value (in USD per share)	$ 0.10	$ 0.10
Common stock, shares authorized (shares)	12,500,000	12,500,000
Common stock, shares issued (shares)	2,905,757	2,905,757
Common stock, shares outstanding (shares)	2,905,757	2,905,757
Non-Voting Common Stock [Member]
Condensed Balance Sheet Statements, Captions [Line Items]
Common stock	$ 1,291	$ 1,291
Total shareholders’ equity	$ 1,291	$ 1,291	$ 1,290	$ 1,289
Common stock, par value (in USD per share)	$ 0.10	$ 0.10
Common stock, shares authorized (shares)	37,500,000	37,500,000
Common stock, shares issued (shares)	12,919,681	12,919,681
Common stock, shares outstanding (shares)	12,919,681	12,919,681
Phi, Inc. and Debtors [Member]
Condensed Balance Sheet Statements, Captions [Line Items]
Cash and cash equivalents	$ 2,781
Short-term investments	73,336
Trade	145,914
Other	5,229
Inventories of spare parts – net	49,963
Prepaid expenses	12,487
Income taxes receivable	942
Total current assets	290,652
Property and equipment – net	856,827
Right of use assets	133,722
Restricted cash and investments	19,789
Other assets	149,142
Total assets	1,450,132
Accounts payable	33,766
Accrued and other current liabilities	44,903
Accrued and other current liabilities	4,750
Current maturities of long term debt	875
Total current liabilities	84,294
Term loan issued March 13, 2019, net of debt issuance costs of $5,609	63,516
Related party term loan issued September 28, 2018, net of debt issuance costs of $656 and $765, respectively	129,344
Deferred income taxes	54,938
Other long-term liabilities	3,324
Long-term operating lease liabilities	109,232
Total liabilities not subject to compromise	360,354
Liabilities subject to compromise	513,125
Total liabilities	957,773
Additional paid-in capital	313,304
Accumulated other comprehensive income (loss)	(3)
Retained earnings	177,477
Total shareholders’ equity	492,359
Total liabilities and shareholders’ equity	1,450,132
Phi, Inc. and Debtors [Member] | Voting Common Stock [Member]
Condensed Balance Sheet Statements, Captions [Line Items]
Common stock	$ 291
Common stock, par value (in USD per share)	$ 0.10
Common stock, shares authorized (shares)	12,500,000
Common stock, shares issued (shares)	2,905,757
Common stock, shares outstanding (shares)	2,905,757
Phi, Inc. and Debtors [Member] | Non-Voting Common Stock [Member]
Condensed Balance Sheet Statements, Captions [Line Items]
Common stock	$ 1,290
Common stock, par value (in USD per share)	$ 0.10
Common stock, shares authorized (shares)	37,500,000
Common stock, shares issued (shares)	12,919,681
Common stock, shares outstanding (shares)	12,919,681
Term Loan [Member]
Condensed Balance Sheet Statements, Captions [Line Items]
Debt issuance costs	$ 5,609	$ 260
Term Loan [Member] | Phi, Inc. and Debtors [Member]
Condensed Balance Sheet Statements, Captions [Line Items]
Debt issuance costs	5,609
Note Payable, Related Party [Member]
Condensed Balance Sheet Statements, Captions [Line Items]
Debt issuance costs	656	$ 765
Note Payable, Related Party [Member] | Phi, Inc. and Debtors [Member]
Condensed Balance Sheet Statements, Captions [Line Items]
Debt issuance costs	$ 656