Detail of Certain Balance Sheet Accounts (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Activity in allowance for doubtful accounts
Balance at beginning of year	$ 4,288	$ 5,158	$ 4,379
Bad debt expense (benefit)	182	(27)	1,552
Deductions for uncollectible receivables written off, net of recoveries	(1,829)	(876)	(798)
Allowance for doubtful accounts of acquired companies at date of acquisition	759	33	25
Balance at end of year	3,400	4,288	$ 5,158
Other current liabilities
Accrued warranty costs	6,149	6,702
Accrued job losses	598	1,269
Accrued sales and use tax	2,308	1,973
Deferred revenue	3,895	5,257
Liabilities due to former owners	2,981	4,196
Other current liabilities	17,723	14,864
Total other current liabilities	$ 33,654	$ 34,261