Fair Value Measurements (Narrative) (Details) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2017	Dec. 31, 2016
Long-term Debt
Transfers between Levels 1 and 2, description	The Company did not have material transfers between Levels 1 and 2 during the three months ended March 31, 2017 or 2016.
Long-term debt, carrying amount	$ 780,789	$ 759,519
2010 Senior Notes [Member]
Long-term Debt
Long-term debt, fair value	304,000	302,600
Long-term debt, carrying amount	298,374	298,120
Convertible Notes [Member]
Long-term Debt
Long-term debt, fair value	249,200	228,400
Long-term debt, carrying amount	$ 154,832	$ 152,668