Debt - Secured Unsecured Notes (Details) - USD ($)	1 Months Ended	3 Months Ended		6 Months Ended
	Aug. 31, 2014	Jun. 30, 2016	Jun. 30, 2015	Jun. 30, 2016	Jun. 30, 2015	Mar. 31, 2015
Debt Instrument [Line Items]
Amortization of deferred financing costs		$ 1,100,000	$ 1,500,000	$ 2,400,000	$ 3,900,000
Convertible Debt | Exchangeable Senior Notes due August 15, 2019
Debt Instrument [Line Items]
Debt instrument face amount	$ 250,000,000.0
Stated rate	2.625%	2.625%		2.625%
Shares converted (in shares)	51.4593
Conversion price (in USD per share)	$ 19.43
Interest expense, debt		$ 2,500,000	2,500,000	$ 4,900,000	4,900,000
Contractual interest expense		1,700,000	1,700,000	3,300,000	3,300,000
Accretion of debt discount		600,000	600,000	1,300,000	1,300,000
Amortization of deferred financing costs		$ 200,000	$ 200,000	$ 300,000	$ 300,000
Senior Notes | Series A, Series B, and Series C Senior Unsecured Notes [Member]
Debt Instrument [Line Items]
Debt instrument face amount						$ 350,000,000
Senior Notes | Series A Senior Notes due 2025
Debt Instrument [Line Items]
Debt instrument face amount						$ 100,000,000
Stated rate		3.93%		3.93%		3.93%
Senior Notes | Series B Senior Notes due 2027
Debt Instrument [Line Items]
Debt instrument face amount						$ 125,000,000
Stated rate		4.09%		4.09%		4.09%
Senior Notes | Series C Senior Notes due 2030
Debt Instrument [Line Items]
Debt instrument face amount						$ 125,000,000
Stated rate		4.18%		4.18%		4.18%