The Company and Summary of Significant Accounting Principles - Recently Adopted - Additional Information (Detail)	3 Months Ended	12 Months Ended
	Mar. 31, 2019 USD ($) Segment	Dec. 31, 2018 Segment
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Right-of-use assets, operating lease	$ 9,041,000
Lease liability, operating lease	$ 9,220,000
Number of reporting segments | Segment	2	1
Number of reporting units | Segment	2
Impairment charges	$ 0
ASU 2016-02 [Member]
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Right-of-use assets, operating lease	10,200,000
Lease liability, operating lease	10,400,000
Right-of-use asset, finance lease	$ 3,400,000