Equity - Convertible Preferred Stock (Details)	9 Months Ended
	Sep. 30, 2018 USD ($) payment director $ / shares Rate shares	Dec. 31, 2017 USD ($) shares
Class of Stock [Line Items]
Preferred stock, shares outstanding | shares	1,495,000	1,495,000
Preferred stock dividend payable | $	$ 14,133,000	$ 10,278,000
Series B Preferred Stock
Class of Stock [Line Items]
Preferred stock, shares outstanding | shares	1,495,000
Series B cumulative convertible perpetual preferred stock interest rate	6.875%
Number of deferred dividend payments | payment	10
Number of additional directors to be elected after threshold of unpaid dividends reached (6 payments) | director	2
Number of trading days	20 days
Number of consecutive trading days	30 days
Closing price as percentage of conversion price | Rate	130.00%
Series B Preferred Stock converted into common stock (in shares) | shares	0.8608
Initial conversion price of common stock (in usd per share) | $ / shares	$ 58.08
Applicable settlement terms	If the Company elects to settle all or any portion of its conversion obligation in cash, the conversion value and the number of shares of the Company’s common stock it will deliver upon conversion (if any) will be based upon a 20 trading day averaging period.
Trading day averaging period for determining conversion value	20 days
Conversion rate numerator for Preferred Stock | $	$ 50
Other long-term liabilities | Series B Preferred Stock
Class of Stock [Line Items]
Preferred stock dividend payable | $	$ 14,100,000