Long-Term Debt - Components of Long-Term Debt (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2016	Dec. 31, 2015	Dec. 31, 2010	Dec. 31, 2009
Debt Instrument [Line Items]
Long-term debt, Amount Outstanding	$ 717,466	$ 624,889
Less unamortized deferred financing costs	(129)	(161)
Total long-term debt, less deferred financing costs	717,337	624,728
Less current portion of long-term debt	(7,849)	(7,423)
Debt classified as long-term debt, less deferred financing costs	$ 709,488	$ 617,305
TDC | Senior Secured Notes, 8.50%
Debt Instrument [Line Items]
Long-term debt, Interest Rate	8.50%	8.50%	8.50%
Long-term debt, Amount Outstanding	$ 17,500	$ 18,750
Interest bearing note, maturity date	Dec. 30, 2020
SDTS Credit Agreements
Debt Instrument [Line Items]
Long-term debt, Amount Outstanding	$ 699,966	$ 606,139
SDTS Credit Agreements | Senior Secured Notes, 5.04%
Debt Instrument [Line Items]
Long-term debt, Interest Rate	5.04%	5.04%
Long-term debt, Amount Outstanding	$ 60,000	$ 60,000
Interest bearing note, maturity date	Jun. 20, 2018
SDTS Credit Agreements | Senior Secured Notes, 3.86%
Debt Instrument [Line Items]
Long-term debt, Interest Rate	3.86%	3.86%
Long-term debt, Amount Outstanding	$ 400,000	$ 400,000
Interest bearing note, maturity date	Dec. 03, 2025
SDTS Credit Agreements | Senior Secured Notes, 3.86% Maturing in 2026
Debt Instrument [Line Items]
Long-term debt, Interest Rate	3.86%
Long-term debt, Amount Outstanding	$ 100,000
Interest bearing note, maturity date	Jan. 14, 2026
SDTS Credit Agreements | Senior Secured Notes, 7.25%
Debt Instrument [Line Items]
Long-term debt, Interest Rate	7.25%	7.25%		7.25%
Long-term debt, Amount Outstanding	$ 42,600	$ 44,512
Interest bearing note, maturity date	Dec. 30, 2029
SDTS Credit Agreements | Senior Secured Notes, 6.47%
Debt Instrument [Line Items]
Long-term debt, Interest Rate	6.47%	6.47%	6.47%
Long-term debt, Amount Outstanding	$ 97,366	$ 101,627
Interest bearing note, maturity date	Sep. 30, 2030