Basis of Presentation and Significant Accounting Policies - Condensed Balance Sheet, Pro Forma Amounts Under Previous Guidance (Details) - USD ($) $ in Thousands	Jun. 30, 2018	Jan. 01, 2018	Dec. 31, 2017
Assets
Contract assets	$ 28,253	$ 29,759	$ 0
Inventories, net	147,186	138,759	162,589
Prepaid expenses and other current assets	14,312	11,513	11,687
Deferred income taxes	7,152	7,811	7,913
Liabilities and Stockholders' Equity
Accounts payable and other current liabilities	296,256	334,463	332,935
Retained earnings	292,936	270,864	266,780
Without Adoption of ASU 2014-09
Assets
Contract assets	0		0
Inventories, net	169,855		162,589
Prepaid expenses and other current assets	14,307		11,687
Deferred income taxes	7,250		7,913
Liabilities and Stockholders' Equity
Accounts payable and other current liabilities	294,484		332,935
Retained earnings	289,217		$ 266,780
Effect of Change \| ASU 2014-09
Assets
Contract assets	28,253	29,759
Inventories, net	(22,669)	(23,830)
Prepaid expenses and other current assets	5	(174)
Deferred income taxes	(98)	(102)
Liabilities and Stockholders' Equity
Accounts payable and other current liabilities	1,772	1,528
Retained earnings	$ 3,719	$ 4,084

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