Income Taxes - Additional Information (Details 5) - USD ($)	12 Months Ended
	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016
Income Taxes
Deferred tax assets, operating loss carryforwards	$ 4,647,000	$ 5,401,000
Credit carry-forwards	16,909,000	10,793,000
Deferred tax asset valuation allowance	8,274,000	8,182,000
Foreign tax credit carry-forwards	7,316,000
Research and development credits	6,516,000
Effects of change in accounting method	0
Effective Income Tax Rate Reconciliation, Change in Enacted Tax Rate, Amount		18,001,000
Foreign income tax expense	12,538,000	7,150,000	$ 13,729,000
Unrecognized tax benefits	6,203,000
Accrued for interest and penalties related to uncertain income tax	$ 2,515,000	2,596,000
Maximum
Income Taxes
Open Tax Year	2010
Minimum
Income Taxes
Open Tax Year	2017
U.S. Federal Tax and Jobs Act Estimate
Income Taxes
Deferred Federal, State and Local, Tax Expense (Benefit)	$ 241,000	6,267,000
Tax Adjustments, Settlements, and Unusual Provisions	589,000	$ 11,734,000
Effective Income Tax Rate Reconciliation, Change in Enacted Tax Rate, Amount	$ 0
Foreign Tax Credit Carryforward | Maximum
Income Taxes [Line Items]
Tax Credit Carryforward, Expiration Date	Dec. 31, 2025
Foreign Tax Credit Carryforward | Minimum
Income Taxes [Line Items]
Tax Credit Carryforward, Expiration Date	Dec. 31, 2023
Research Tax Credit Carryforward [Member] | Maximum
Income Taxes [Line Items]
Tax Credit Carryforward, Expiration Date	Dec. 31, 2038
Research Tax Credit Carryforward [Member] | Minimum
Income Taxes [Line Items]
Tax Credit Carryforward, Expiration Date	Dec. 31, 2021
Operating Loss Carryforward [Member] | Maximum
Income Taxes [Line Items]
Tax Credit Carryforward, Expiration Date	Dec. 31, 2038
Operating Loss Carryforward [Member] | Minimum
Income Taxes [Line Items]
Tax Credit Carryforward, Expiration Date	Dec. 31, 2021