Consolidated Statements of Cash Flows - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2021	Dec. 31, 2020	Dec. 31, 2019
OPERATING ACTIVITIES:
Net income	$ 49,432	$ 66,103	$ 49,339
Loss from discontinued operations, net of income taxes			(6,329)
INCOME FROM CONTINUING OPERATIONS	49,432	66,103	55,668
Adjustments to reconcile net income to net cash flows provided by operating activities:
Depreciation expense	43,016	38,183	37,145
Deferred income taxes	12,311	20,508	15,134
(Gain) loss on dispositions of property and equipment	(294)	(1,571)	1,138
Amortization of deferred financing fees	2,349	1,611	2,746
Share-based compensation expense	5,188	6,754	6,908
Changes in assets and liabilities:
Accounts receivable	(43,963)	(19,205)	44,994
Contract revenues in excess of billings	(7,738)	(9,546)	(4,607)
Inventories	(2,706)	(2,383)	(1,939)
Prepaid expenses and other current assets	10,873	1,466	(8,539)
Accounts payable and accrued expenses	(698)	(3,328)	12,546
Billings in excess of contract revenues	(17,794)	(22,658)	37,473
Other noncurrent assets and liabilities	(969)	3,013	3,120
Net cash flows provided by operating activities of continuing operations	49,007	78,947	201,787
Net cash flows used in operating activities of discontinued operations			(9,238)
Cash provided by operating activities	49,007	78,947	192,549
INVESTING ACTIVITIES:
Purchases of property and equipment	(116,658)	(47,621)	(49,412)
Proceeds from dispositions of property and equipment	4,459	4,450	5,592
Net cash flows used in investing activities of continuing operations	(112,199)	(43,171)	(43,820)
Net cash flows provided by investing activities of discontinued operations			18,056
Cash used in investing activities	(112,199)	(43,171)	(25,764)
FINANCING ACTIVITIES:
Repayments of debt	(325,000)
Proceeds from issuance of debt	325,000
Deferred financing fees	(4,395)		(2,388)
Taxes paid on settlement of vested share awards	(3,785)	(4,748)	(5,008)
Exercise of stock options and purchases from employee stock plans	2,321	2,360	4,839
Repurchase of common stock		(3,873)
Repayments of revolving loans			(11,500)
Net cash flows used in financing activities of continuing operations	(5,859)	(6,261)	(14,057)
Net cash flows used in financing activities of discontinued operations			(191)
Cash used in financing activities	(5,859)	(6,261)	(14,248)
Net (decrease) increase in cash, cash equivalents and restricted cash	(69,051)	29,515	152,537
Cash, cash equivalents and restricted cash at beginning of period	216,510	186,995	34,458
Cash, cash equivalents and restricted cash at end of period	147,459	216,510	186,995
Cash and cash equivalents	145,459	216,510	186,995
Restricted cash included in other long-term assets	2,000
Supplemental Cash Flow Information
Cash paid for interest	22,919	26,430	24,942
Cash paid for income taxes	637	392	366
Non-cash Investing and Financing Activities
Property and equipment purchased but not yet paid	$ 7,010	$ 6,693	$ 6,473