Commitments and Contingencies - Additional Information (Details) - USD ($)		3 Months Ended	9 Months Ended
	Nov. 02, 2017	Jun. 30, 2016	Sep. 30, 2018	Dec. 31, 2017
Commitments And Contingencies [Line Items]
Redemption of Series B preferred stock at face value plus accrued dividends			$ 172,882,000	$ 165,581,000
Income tax examination, liability settled			$ 300,000
State Tax Assessment
Commitments And Contingencies [Line Items]
Tax assessment period			2010 2011 2012 2013
State Tax Assessment | Tax Year 2014
Commitments And Contingencies [Line Items]
Open tax year			2014 2015 2016 2017
Local Jurisdiction
Commitments And Contingencies [Line Items]
Income tax examination, liability settled			$ 200,000
Local Tax Assessment
Commitments And Contingencies [Line Items]
Tax assessment period, beginning date			Jun. 01, 2005
Tax assessment period, ending date			May 31, 2015
Proposed underpaid tax, applicable interest and penalties amount			$ 1,439,452
Local tax assessment, estimated probable loss		$ 391,000
Series B Preferred Stock Litigation
Commitments And Contingencies [Line Items]
Claiming percentage of litigation	94.16%
Redemption of Series B preferred stock at face value plus accrued dividends			$ 172,900,000
Loss contingency, description of damages sought			The complaint requests relief including, among other things, an order interpreting and enforcing the Certificate of Designations, preventing us from making any additional payments on the Notes and requiring us to redeem the Series B preferred stock at face value plus accrued dividends (or approximately $172.9 million as of September 30, 2018), as well as unspecified money damages and a declaration that Section 10.4 of the Charter is invalid.
Gutierrez-Ortiz Lawsuit
Commitments And Contingencies [Line Items]
Damages sought value			$ 3,500,000
Settlement amount			$ 75,000