Restatement of Previously Issued Financial Statements (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended				6 Months Ended	9 Months Ended	12 Months Ended
	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Jun. 30, 2014	Sep. 30, 2014	Dec. 31, 2014	Dec. 31, 2013	Dec. 31, 2012	Dec. 31, 2011
Balance Sheets
Deferred tax assets	$ 50	$ 49				$ 49	$ 50
Total current assets	473,382	461,624	$ 441,318		$ 441,318	461,624	473,382	$ 217,400
Deferred tax assets, non-current	4,467	4,404				4,404	4,467
Total assets	479,786	467,683	457,654		457,654	467,683	479,786	217,682
Income taxes payable		7,785	29,559		29,559	7,785
Total current liabilities	19,831	24,039	35,381		35,381	24,039	19,831	6,295
Total liabilities	351,249	314,591	318,714		318,714	314,591	351,249	47,962
Accumulated deficit	(299,822)	(268,170)	(276,722)		(276,722)	(268,170)	(299,822)	(183,050)
Total stockholders' equity	128,537	153,092	138,940		138,940	153,092	128,537	169,720	$ (123,470)	$ (102,487)
Total liabilities and stockholders' equity	479,786	467,683	457,654		457,654	467,683	479,786	217,682
Statements of Operations
Income tax provision	512	5,179	30,785		30,785	35,964	36,476
Net income (loss)	$ (31,652)	$ 8,552	$ (72,990)		$ (93,672)	$ (85,120)	$ (116,772)	(51,145)	(14,562)
Basic(in dollars per share)	$ (0.94)	$ 0.26	$ (2.19)	$ (0.64)	$ (2.85)	$ (2.57)	$ (3.51)
Diluted( in dollars per share)	$ (0.94)	$ 0.25	$ (2.19)	$ (0.64)	$ (2.85)	$ (2.57)	$ (3.51)
Statements Comprehensive Income (Loss)
Net income (loss)	$ (31,652)	$ 8,552	$ (72,990)		$ (93,672)	$ (85,120)	$ (116,772)	(51,145)	(14,562)
Comprehensive income (loss)		8,562	(72,983)		(93,647)	(85,085)	(116,837)	(51,145)	(14,562)
Statements of Cash Flows
Net loss	(31,652)	8,552	(72,990)		(93,672)	(85,120)	(116,772)	$ (51,145)	$ (14,562)
Deferred income taxes					1,226	(2,144)	(214)
Income taxes payable					29,559	7,785
Previously reported
Balance Sheets
Deferred tax assets	293	1,069	837		837	1,069	293
Total current assets	473,625	462,644	442,155		442,155	462,644	473,625
Deferred tax assets, non-current	22,808	26,187	19,635		19,635	26,187	22,808
Total assets	498,370	490,486	478,126		478,126	490,486	498,370
Income taxes payable		7,785	29,540		29,540	7,785
Total current liabilities	19,831	24,039	35,362		35,362	24,039	19,831
Total liabilities	351,249	314,591	318,695		318,695	314,591	351,249
Accumulated deficit	(281,238)	(245,367)	(256,231)		(256,231)	(245,367)	(281,238)
Total stockholders' equity	147,121	175,895	159,431		159,431	175,895	147,121
Total liabilities and stockholders' equity	498,370	490,486	478,126		478,126	490,486	498,370
Statements of Operations
Income tax provision	4,731	2,867	10,294		10,294	13,161	17,892
Net income (loss)	$ (35,871)	$ 10,864	$ (52,499)		$ (73,181)	$ (62,317)	$ (98,188)
Basic(in dollars per share)	$ (1.06)	$ 0.32	$ (1.57)		$ (2.23)	$ (1.88)	$ (2.95)
Diluted( in dollars per share)	$ (1.06)	$ 0.31	$ (1.57)		$ (2.23)	$ (1.88)	$ (2.95)
Statements Comprehensive Income (Loss)
Net income (loss)	$ (35,871)	$ 10,864	$ (52,499)		$ (73,181)	$ (62,317)	$ (98,188)
Comprehensive income (loss)		10,874	(52,492)		(73,156)	(62,282)	(98,253)
Statements of Cash Flows
Net loss	$ (35,871)	$ 10,864	$ (52,499)		(73,181)	(62,317)	(98,188)
Deferred income taxes					(19,246)	(24,947)	$ (18,798)
Income taxes payable					$ 29,540	$ 7,785