Long-Term Debt - Schedule of Interest Expense Related To Debt (Details) - USD ($)	3 Months Ended		6 Months Ended
	Jun. 30, 2018	Jun. 30, 2017	Jun. 30, 2018	Jun. 30, 2017
Debt Disclosure [Abstract]
Interest expense	$ 10,803,000	$ 9,202,000	$ 21,051,000	$ 18,225,000
Amortization of debt issuance costs related to long-term debt, including our credit facility	734,000	830,000	1,566,000	1,673,000
Commitment fees	707,000	774,000	1,324,000	1,561,000
Interest costs capitalized	$ 0	$ 0	$ 0	$ 0
Unused capacity, commitment fee percentage			0.30%