Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2017	Sep. 30, 2016
Operating Activities
Net income	$ 76,829	$ 55,217
Adjustments to reconcile net income to net cash provided by operating activities:
Depreciation and amortization	12,065	10,893
Stock-based compensation	3,913	3,806
Loss (gain) on disposal of property, plant and equipment	1,720	(189)
Other non-cash adjustments	(405)	(285)
Changes in operating assets and liabilities:
Accounts receivable	(14,407)	1,580
Contract retainage	55
Inventories	4,860	6,597
Prepaid expenses and other assets	2,987	(771)
Revenues in excess of billings	(1,243)
Accounts payable	1,203	(6,761)
Accrued expenses and other liabilities	(1,430)	5,005
Billings in excess of revenues	(399)
Customer deposits	(609)
Income taxes receivable/payable	7,698	8,487
Net cash provided by operating activities	92,837	83,579
Investing Activities
Expenditures for property, plant and equipment	(11,108)	(8,534)
Proceeds from sales of property, plant and equipment		4,349
Acquisition of business	(71,523)
Net cash used in investing activities	(82,631)	(4,185)
Financing Activities
Borrowings under line of credit	201,000	242,700
Principal payments under line of credit	(201,000)	(249,700)
Repurchases of common stock	(3,617)	(55,185)
Financing costs		(485)
Proceeds from employee stock purchase and option plans	288	218
Net cash used in financing activities	(3,329)	(62,452)
Net increase in cash and cash equivalents	6,877	16,942
Cash and cash equivalents, beginning of period	18,664	5,995
Cash and cash equivalents, end of period	25,541	22,937
Supplemental Disclosure:
Cash paid for interest	416	849
Cash paid for income taxes, net	$ 32,016	$ 19,435