Convertible Senior Notes (Due 2017) (Details)	1 Months Ended	3 Months Ended
	Jun. 30, 2012 USD ($) d $ / shares	Mar. 31, 2016 USD ($)	Mar. 31, 2015 USD ($)	Dec. 31, 2015 USD ($)
Interest expense
Amortization of debt discount		$ 6,300,000	$ 5,516,000
Senior Notes [Member] | Convertible Senior Notes Due 2017 [Member]
Debt Instrument [Line Items]
Aggregate principal amount	$ 275,000,000	275,000,000		$ 275,000,000
Interest rate	1.375%
Proceeds from offering	$ 266,200,000
Trading period | d	20
Consecutive trading period	30 days
Redemption stock price conversion threshold (greater than or equal to)	130.00%
Consecutive measurement period	5 days
Percent of trading price (less than)	98.00%
Conversion ratio	0.0358038
Conversion price (USD per share) | $ / shares	$ 27.93
Percent of principal amount plus accrued and unpaid interest	100.00%
Debt default principal amount percentage	25.00%
Debt instrument, term	5 years
Carrying amount of equity component		55,700,000
Deferred tax asset, hedging	$ 1,500,000
Liability component
Principal	$ 275,000,000	275,000,000		275,000,000
Less: Debt discount, net		(16,200,000)		(19,527,000)
Net carrying amount		258,800,000		$ 255,473,000
Fair value of Notes		$ 270,700,000
Remaining contractual life		1 year 2 months 12 days
Interest expense
Contractual interest expense		$ 945,000	945,000
Amortization of debt discount		3,327,000	3,113,000
Total		$ 4,272,000	$ 4,058,000
Effective interest rate of the liability component		6.02%	6.02%