Income Taxes - Additional Information (Details 5) - USD ($)	12 Months Ended
	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Income Taxes
Deferred tax assets, operating loss carryforwards	$ 5,401,000	$ 7,279,000
Credit carry-forwards	10,793,000	22,743,000
Deferred tax asset valuation allowance	8,182,000	11,024,000
Foreign tax credit carry-forwards	3,711,000
Research and development credits	7,249,000
Effective Income Tax Rate Reconciliation, Change in Enacted Tax Rate, Amount	18,001,000
Foreign income tax expense	7,150,000	13,729,000	$ 12,482,000
Income tax provision on foreign earnings to be permanently reinvested outside US	370,000
Unrecognized tax benefits	7,306,000
Accrued for interest and penalties related to uncertain income tax	$ 2,596,000	$ 1,772,000
Maximum
Income Taxes
Open Tax Year	2008
Minimum
Income Taxes
Open Tax Year	2016
Non-U.S. | Income Tax Benefit
Income Taxes
Effects of change in accounting method			16,305,000
Non-U.S. | Operating Carry Forward
Income Taxes
Effects of change in accounting method			(8,214,000)
Non-U.S. | Foreign Tax Credit Carryforward
Income Taxes
Effects of change in accounting method			$ 24,519,000
U.S. Federal Tax and Jobs Act Estimate
Income Taxes
Deferred Federal, State and Local, Tax Expense (Benefit)	$ 6,267,000
Tax Adjustments, Settlements, and Unusual Provisions	$ 11,734,000
Foreign Tax Credit Carryforward | Maximum
Income Taxes
Tax Credit Carryforward, Expiration Date	Dec. 31, 2025
Foreign Tax Credit Carryforward | Minimum
Income Taxes
Tax Credit Carryforward, Expiration Date	Dec. 31, 2024
Research Tax Credit Carryforward [Member] | Maximum
Income Taxes
Tax Credit Carryforward, Expiration Date	Dec. 31, 2037
Research Tax Credit Carryforward [Member] | Minimum
Income Taxes
Tax Credit Carryforward, Expiration Date	Dec. 31, 2022