Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020
OPERATING ACTIVITIES:
Net income	$ 10,919	$ 42,947
Adjustments to reconcile net income to net cash flows provided by operating activities:
Depreciation and amortization	20,681	18,707
Deferred income taxes	2,218	14,441
Gain on sale of assets	(32)	(184)
Amortization of deferred financing fees	1,715	805
Share-based compensation expense	2,564	3,130
Changes in assets and liabilities:
Accounts receivable	3,249	(14,109)
Contract revenues in excess of billings	(2,450)	2,123
Inventories	(1,233)	(4,733)
Prepaid expenses and other current assets	4,131	10,733
Accounts payable and accrued expenses	(2,668)	(8,229)
Billings in excess of contract revenues	(3,775)	(179)
Other noncurrent assets and liabilities	282	2,008
Cash provided by operating activities	35,601	67,460
INVESTING ACTIVITIES:
Purchases of property and equipment	(64,828)	(21,076)
Proceeds from dispositions of property and equipment	223	936
Cash used in investing activities	(64,605)	(20,140)
FINANCING ACTIVITIES:
Deferred financing fees	(4,395)
Taxes paid on settlement of vested share awards	(3,784)	(2,106)
Exercise of options and purchases from employee stock plans	1,440	1,318
Cash used in financing activities	(6,739)	(788)
Net (decrease) increase in cash, cash equivalents and restricted cash	(35,743)	46,532
Cash, cash equivalents and restricted cash at beginning of period	216,510	186,995
Cash, cash equivalents and restricted cash at end of period	180,767	233,527
Supplemental Cash Flow Information
Cash paid for interest	13,984	12,548
Cash paid for income taxes	332	175
Non-cash Investing and Financing Activities
Property and equipment purchased but not yet paid	$ 11,139	$ 4,608