Income Taxes - Additional Information (Details) - USD ($)	1 Months Ended	12 Months Ended			24 Months Ended
	May 31, 2017	Dec. 31, 2018	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2018
Income Tax Disclosure [Line Items]
U.S. federal corporate tax rate		21.00%	35.00%	35.00%
Tax Cuts and Jobs Act of 2017, accounting complete true or false		true
Transition tax expense		$ 126,000	$ 574,000	$ 0
Final transition tax liability		$ 700,000			$ 700,000
Percentage of transition tax liability impact on effective tax rate		0.10%	1.00%	0.00%
Provisional tax benefit			$ 3,400,000
Final tax benefit		$ 195,000	$ 3,418,000	$ 0	3,600,000
Percentage of tax benefit from adjustment of deferred tax assets and liabilities		0.20%	6.00%	0.00%
Deferred tax liability not recognized from undistributed earnings of foreign subsidiaries		$ 0			0
Deduction for dividends received in tax reform act		100.00%
Dividends received from owned foreign corporations by us corporate shareholders		10.00%
Foreign corporations shareholders holding period		1 year
Amount of undistributed earnings of foreign subsidiaries for which deferred foreign withholding taxes not recorded		$ 21,100,000			21,100,000
Deferred tax assets, foreign operating loss carryforwards		248,000	$ 246,000		248,000
Deferred tax assets, valuation allowance		$ 169,000	2,394,000		169,000
Percentage of foreign net operating loss carryforward		59.00%
Deferred tax assets			21,100,000
Deferred tax liabilities			100,000
Liability for interest and penalties		$ 1,000,000.0	1,400,000		1,000,000.0
Liability for uncertain tax position		$ 7,200,000	$ 5,900,000		7,200,000
Number of tax years		4 years
IRC Section 382 Ownership Shift
Income Tax Disclosure [Line Items]
Disposal of deferred tax assets		$ 7,400,000
Reduction in deferred credit		6,900,000
Net increase in tax expense		$ 500,000
NephroGenex, Inc.
Income Tax Disclosure [Line Items]
Deferred tax assets	$ 22,200,000
Tax effected net operating losses	13,500,000
Tax effected capitalized research and development expenses	8,500,000
Tax effected federal tax credits	200,000
Deferred tax liabilities	$ 100,000
Minimum
Income Tax Disclosure [Line Items]
Foreign net operating loss carryforwards expiration year		2020
Maximum
Income Tax Disclosure [Line Items]
Foreign net operating loss carryforwards expiration year		2027
U.S. State and Local
Income Tax Disclosure [Line Items]
Tax credits carryforward expiration year		2023
Foreign Tax Authority
Income Tax Disclosure [Line Items]
Deferred tax assets, valuation allowance		$ 200,000			$ 200,000
Foreign, State and Local Jurisdictions | Earliest Tax Year
Income Tax Disclosure [Line Items]
Open tax year		2014
Foreign, State and Local Jurisdictions | Latest Tax Year
Income Tax Disclosure [Line Items]
Open tax year		2018
Federal | Earliest Tax Year
Income Tax Disclosure [Line Items]
Open tax year		2015
Federal | Latest Tax Year
Income Tax Disclosure [Line Items]
Open tax year		2018