Summary of Significant Accounting Policies (Summary of Reclassification Adjustments) (Details) - USD ($) $ in Thousands		3 Months Ended	6 Months Ended	9 Months Ended	12 Months Ended
		Mar. 31, 2016	Jun. 30, 2016	Sep. 30, 2016	Dec. 31, 2016		Dec. 31, 2015		Dec. 31, 2014		Dec. 31, 2013	[1]
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Cash and cash equivalents		$ 7,824	$ 65,378	$ 72,855	$ 82,584	[1],[2]	$ 7,925	[1],[2]	$ 24,017	[1]	$ 49,032
Change in short-term investments	[1]						6,995		1,810
Net cash from investing activities		(3,058)	101,376	96,122	93,351		(33,589)		(406,756)
Change in cash and cash equivalents		(101)	57,453	64,930	74,659	[1]	(16,092)	[1]	(25,015)	[1]
Cash and cash equivalents at beginning of year		7,925	7,925	7,925	7,925		24,017		49,032
Cash and cash equivalents at end of year		7,824	65,378	72,855			7,925		24,017
Previously Reported [Member]
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Cash		7,789	25,301	32,734			7,886
Short-term investments		35	40,077	40,121			39
Change in short-term investments		(4)	40,038	40,082			26,329		25,883
Net cash from investing activities		(3,054)	61,338	56,040			(14,255)		(382,683)
Change in cash and cash equivalents		(97)	17,415	24,848			3,242		(942)
Cash and cash equivalents at beginning of year		7,886	7,886	7,886	7,886		4,644		5,586
Cash and cash equivalents at end of year		7,789	25,301	32,734			7,886		4,644
Effect of Change [Member]
New Accounting Pronouncements Or Change In Accounting Principle [Line Items]
Cash and cash equivalents		7,824	65,378	72,855			7,925
Cash		(7,789)	(25,301)	(32,734)			(7,886)
Short-term investments		(35)	(40,077)	(40,121)			(39)
Change in short-term investments		4	(40,038)	(40,082)			(19,334)		(24,073)
Net cash from investing activities		(4)	40,038	40,082			(19,334)		(24,073)
Change in cash and cash equivalents		(4)	40,038	40,082			(19,334)		(24,073)
Cash and cash equivalents at beginning of year		39	39	39	$ 39		19,373		43,446
Cash and cash equivalents at end of year		$ 35	$ 40,077	$ 40,121			$ 39		$ 19,373

[1] Certain short-term investments in 2015 and 2014 were reclassified to cash and cash equivalents to conform with the 2016 presentation.

[2] Short-term investments as of December 31, 2015 were reclassified to cash and cash equivalents to conform with the 2016 presentation.