Condensed Consolidating Financial Information - Guarantor Subsidiaries - Condensed Consolidating Balance Sheets (Detail) - USD ($)	Dec. 31, 2017	Dec. 29, 2017	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2014
Current Assets:
Cash	$ 8,770,000		$ 2,596,000	$ 2,407,000	$ 6,270,000
Short-term investments	64,237,000		289,806,000
Accounts receivable - net	185,979,000		138,265,000
Inventories of spare parts – net	80,881,000		70,402,000
Prepaid expenses	11,475,000		9,259,000
Deferred income taxes	0		10,798,000
Income taxes receivable	1,271,000		540,000
Total current assets	352,613,000		521,666,000
Property and equipment – net	946,765,000		903,977,000
Restricted cash and investments	12,396,000		13,038,000
Other assets	8,741,000		9,759,000
Deferred income taxes	3,309,000		0
Goodwill	61,299,000	$ 61,299	0
Intangibles	16,723,000		0
Total assets	1,401,846,000		1,448,440,000
Current Liabilities:
Accounts payable	37,186,000		28,704,000
Accrued and other current liabilities	41,850,000		28,346,000
Total current liabilities	79,036,000		57,050,000
Long-term debt	615,994,000		631,247,000
Deferred income taxes and other long-term liabilities	94,162,000		160,365,000
Shareholders’ Equity:
Common stock and paid-in capital	309,933,000		305,815,000
Accumulated other comprehensive loss	(280,000)		(478,000)
Retained earnings	303,001,000		294,441,000
Total shareholders’ equity	612,654,000		599,778,000	626,998,000	597,068,000
Total liabilities and shareholders’ equity	1,401,846,000		1,448,440,000
Parent Company Only (issuer) [Member]
Current Assets:
Cash	47,000		36,000	46,000	51,000
Short-term investments	64,237,000		289,806,000
Accounts receivable - net	90,077,000		71,458,000
Inventories of spare parts – net	68,737,000		61,834,000
Prepaid expenses	8,348,000		6,990,000
Deferred income taxes			10,798,000
Income taxes receivable	345,000		558,000
Total current assets	231,791,000		441,480,000
Investment in subsidiaries and others	397,301,000		353,160,000
Property and equipment – net	617,488,000		589,104,000
Restricted cash and investments	12,382,000		13,023,000
Other assets	139,754,000		8,660,000
Total assets	1,398,716,000		1,405,427,000
Current Liabilities:
Accounts payable	28,130,000		22,744,000
Accrued and other current liabilities	23,147,000		18,725,000
Intercompany payable	113,387,000		57,904,000
Total current liabilities	164,664,000		99,373,000
Long-term debt	615,994,000		631,247,000
Deferred income taxes and other long-term liabilities	5,404,000		75,029,000
Shareholders’ Equity:
Common stock and paid-in capital	309,933,000		305,815,000
Accumulated other comprehensive loss	(280,000)		(478,000)
Retained earnings	303,001,000		294,441,000
Total shareholders’ equity	612,654,000		599,778,000
Total liabilities and shareholders’ equity	1,398,716,000		1,405,427,000
Guarantor Subsidiaries [Member]
Current Assets:
Cash	1,072,000		2,100,000	1,672,000	5,966,000
Accounts receivable - net	74,886,000		62,868,000
Intercompany receivable	126,366,000		91,040,000
Inventories of spare parts – net	9,049,000		8,568,000
Prepaid expenses	1,898,000		2,184,000
Income taxes receivable	9,000		(18,000)
Total current assets	213,280,000		166,742,000
Property and equipment – net	284,984,000		294,197,000
Other assets	908,000		1,099,000
Total assets	499,172,000		462,038,000
Current Liabilities:
Accounts payable	4,636,000		5,822,000
Accrued and other current liabilities	10,577,000		9,418,000
Total current liabilities	15,213,000		15,240,000
Deferred income taxes and other long-term liabilities	84,300,000		85,336,000
Shareholders’ Equity:
Common stock and paid-in capital	77,951,000		77,951,000
Retained earnings	321,708,000		283,511,000
Total shareholders’ equity	399,659,000		361,462,000
Total liabilities and shareholders’ equity	499,172,000		462,038,000
Non-Guarantor Subsidiaries [Member]
Current Assets:
Cash	7,651,000		460,000	689,000	253,000
Accounts receivable - net	38,020,000		3,939,000
Intercompany receivable			(33,136,000)
Inventories of spare parts – net	3,095,000
Prepaid expenses	1,229,000		85,000
Income taxes receivable	917,000
Total current assets	50,912,000		(28,652,000)
Property and equipment – net	44,293,000		20,676,000
Restricted cash and investments	14,000		15,000
Other assets	(131,921,000)
Deferred income taxes	3,309,000
Goodwill	61,299,000
Intangibles	16,723,000
Total assets	44,629,000		(7,961,000)
Current Liabilities:
Accounts payable	21,425,000		138,000
Accrued and other current liabilities	8,126,000		203,000
Intercompany payable	12,978,000
Total current liabilities	42,529,000		341,000
Deferred income taxes and other long-term liabilities	4,458,000
Shareholders’ Equity:
Common stock and paid-in capital	1,375,000		1,240,000
Retained earnings	(3,733,000)		(9,542,000)
Total shareholders’ equity	(2,358,000)		(8,302,000)
Total liabilities and shareholders’ equity	44,629,000		(7,961,000)
Eliminations [Member]
Current Assets:
Cash	0		0	$ 0	$ 0
Accounts receivable - net	(17,004,000)
Intercompany receivable	(126,366,000)		(57,904,000)
Total current assets	(143,370,000)		(57,904,000)
Investment in subsidiaries and others	(397,301,000)		(353,160,000)
Total assets	(540,671,000)		(411,064,000)
Current Liabilities:
Accounts payable	(17,005,000)
Intercompany payable	(126,365,000)		(57,904,000)
Total current liabilities	(143,370,000)		(57,904,000)
Shareholders’ Equity:
Common stock and paid-in capital	(79,326,000)		(79,191,000)
Retained earnings	(317,975,000)		(273,969,000)
Total shareholders’ equity	(397,301,000)		(353,160,000)
Total liabilities and shareholders’ equity	$ (540,671,000)		$ (411,064,000)