Derivative Instruments (Narrative) (Details) $ / shares in Units, $ in Thousands		1 Months Ended	3 Months Ended								12 Months Ended			13 Months Ended
	Sep. 15, 2015 USD ($)	Sep. 30, 2010 USD ($) counterparties $ / shares shares	Dec. 31, 2016 USD ($)	Sep. 30, 2016 USD ($)	Jun. 30, 2016 USD ($)	Mar. 31, 2016 USD ($)	Dec. 31, 2015 USD ($) shares	Sep. 30, 2015 USD ($)	Jun. 30, 2015 USD ($)	Mar. 31, 2015 USD ($)	Dec. 31, 2016 USD ($) shares	Dec. 31, 2015 USD ($) $ / shares shares	Dec. 31, 2014 USD ($) partial_unwind_agreement	Dec. 31, 2016 USD ($) shares
Derivative Instruments and Hedging Activities Disclosure [Abstract]
Derivative collateral			$ 827,800				$ 349,800				$ 827,800	$ 349,800		$ 827,800
Credit risk, maximum exposure											55,500	36,900
Number of partial unwind agreements | partial_unwind_agreement													5
Net cash received from counterparties for settlement of call options and warrants													$ 16,600
Warrants reclassified from equity to a derivative liability, at fair value													(51,257)
Derivative [Line Items]
Change in fair value of embedded derivatives											(543,465)	464,698	(32,321)
Net income			120,796	$ (7,420)	$ 14,708	$ (44,841)	$ 33,776	$ 97,306	$ 82,845	$ 5,903	$ 83,243	$ 219,830	126,023
Shares of common stock issued to settle warrants that have reached their expiration | shares											92,998	47,868		140,866
2015 Notes Hedges [Member]
Derivative [Line Items]
Number of counterparties | counterparties		2
Conversion spread, shares of common stock | shares		16,000,000
Derivative asset, strike price | $ / shares		$ 12.50
Derivative asset, cash received to settle	$ 25,800
2015 Notes Embedded Conversion Derivative [Member]
Derivative [Line Items]
Change in fair value of embedded derivatives											$ 0	$ 4,516	19,036
Derivative liability, cash paid to settle conversion premium	$ 25,800
2015 Warrants [Member]
Derivative [Line Items]
Number of securities called by warrants | shares		16,000,000					1,600,000					1,600,000
Warrants, exercise price | $ / shares		$ 16.00										$ 15.59
Proceeds from issuance of warrants		$ 15,600
September 2015 Notes [Member]
Derivative [Line Items]
Debt instrument, face amount		$ 200,000
Interest rate		3.50%
SunTrust [Member] | Not Designated as Hedging Instrument [Member]
Derivative [Line Items]
Collateral on deposit			$ 700								$ 700			$ 700
SunTrust [Member] | Not Designated as Hedging Instrument [Member] | Interest Rate Swap [Member]
Derivative [Line Items]
Derivative, term of contract											7 years
SunTrust [Member] | Not Designated as Hedging Instrument [Member] | Interest Rate Caps [Member]
Derivative [Line Items]
Derivative, term of contract											7 years
SunTrust [Member] | Three Month London Interbank Offered Rate (LIBOR) [Member] | Not Designated as Hedging Instrument [Member]
Derivative [Line Items]
Cap rate			2.50%								2.50%			2.50%
Change in Assumptions for Fair Value [Member]
Derivative [Line Items]
Change in fair value of embedded derivatives													(62,600)
Net income													$ 14,800
Call Options [Member]
Derivative [Line Items]
Investment maturity period											1 year