Significant Accounting Policies (Detail)	3 Months Ended		12 Months Ended
	Mar. 31, 2019 USD ($)	Dec. 31, 2018 USD ($)	Dec. 31, 2019 USD ($) Project	Dec. 31, 2018 USD ($) Project	Dec. 31, 2017 USD ($)
Accounting Policies [Line Items]
Reclassified from engineering cost to product development cost				$ 19,100,000	$ 22,200,000
Reclassification from selling, general and administrative to cost of sales				2,900,000	2,700,000
Inventory reserves		$ 108,567,000	$ 71,020,000	108,567,000
Impairments		38,600,000	0	38,559,000
Restructuring and other charges				60,000,000.0
Severance costs	$ 1,100,000		0	7,300,000
Inventory write-down				32,100,000
Long-lived asset impairment		38,600,000		14,900,000
Restructuring costs			4,400,000	5,700,000
Unbilled receivables		83,502,000	$ 140,534,000	$ 83,502,000
Number of projects | Project			36	22
Percentage of total revenues			20.50%	16.00%
Percentage of product revenues			28.00%	23.00%
Gain (loss) in foreign currency exchange transactions			$ 1,300,000	$ 800,000	$ (12,700,000)
Over Time Method
Accounting Policies [Line Items]
Unbilled receivables		57,000,000.0	83,200,000	57,000,000.0
Chief Operating Officer
Accounting Policies [Line Items]
Severance costs	$ 1,100,000
Inventories
Accounting Policies [Line Items]
Inventory reserves		$ 108,600,000	71,000,000.0	$ 108,600,000
Impairments			$ 0