Basis of Presentation and Significant Accounting Policies - Condensed Balance Sheet, Pro Forma Amounts Under Previous Guidance (Details) - USD ($) $ in Thousands	Sep. 30, 2018	Jan. 01, 2018	Dec. 31, 2017
Assets
Contract assets	$ 26,257	$ 29,759	$ 0
Inventories, net	135,888	138,759	162,589
Prepaid expenses and other current assets	15,429	11,513	11,687
Deferred income taxes	7,371	7,811	7,913
Liabilities and Equity
Accounts payable and other current liabilities	273,347	334,463	332,935
Retained earnings	293,895	270,864	266,780
Without Adoption of ASU 2014-09
Assets
Contract assets	0		0
Inventories, net	156,553		162,589
Prepaid expenses and other current assets	15,419		11,687
Deferred income taxes	7,379		7,913
Liabilities and Equity
Accounts payable and other current liabilities	271,734		332,935
Retained earnings	289,914		$ 266,780
Effect of Change \| ASU 2014-09
Assets
Contract assets	26,257	29,759
Inventories, net	(20,665)	(23,830)
Prepaid expenses and other current assets	10	(174)
Deferred income taxes	(8)	(102)
Liabilities and Equity
Accounts payable and other current liabilities	1,613	1,528
Retained earnings	$ 3,981	$ 4,084

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