Leases (Details) - USD ($) $ in Thousands	3 Months Ended	12 Months Ended
	Mar. 31, 2019	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Lessee, Lease, Description [Line Items]
Operating	$ 6,686
Current Operating	2,434
Noncurrent Operating	4,631
Total lease liabilities	7,065
Lease Costs
Operating lease costs	589
Short-term lease costs	303
Sublease income	(24)
Net lease costs	868
Cash paid for amounts included in the measurement of lease liabilities, Operating cash flows from operating leases	565
Right-of-use assets obtained in exchange for lease obligations, Operating	$ 576
Weighted average discount rate, Operating leases	5.88%
Weighted average remaining lease term, Operating leases	3 years 3 months 18 days
Maturities of Operating Lease Liabilities
2019	$ 2,168
2020	2,278
2021	1,684
2022	1,079
2023	496
After 2023	57
Total lease payments	7,762
Less interest	697
Total operating lease liability	$ 7,065
Rental payments, minimum rentals and rental expenses		$ 2,081	$ 2,372	$ 2,561
Annual commitments under non-cancellable operating leases, next five years		6,897
Annual commitments under non-cancellable operating lease, after 5 years		55
Maturity of Operating Lease Liabilities
2019		2,224
2020		1,858
2021		1,357
2022		977
2023		481
After 2023		55
Total lease commitments		$ 6,952
Minimum
Lessee, Lease, Description [Line Items]
Remaining lease terms	1 year
Maximum
Lessee, Lease, Description [Line Items]
Remaining lease terms	5 years