Senior Convertible Notes (Details Textual) (USD $)	3 Months Ended		6 Months Ended			12 Months Ended
	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2014	Jun. 30, 2013	Jun. 30, 2011	Dec. 31, 2011	Dec. 31, 2013
Senior Convertible Notes (Textual) [Abstract]
Debt Instrument, convertible carrying amount	$ 49,300,000		$ 49,300,000			$ 49,300,000
2.75% Senior Convertible Notes due 2017 [Member]
Senior Convertible Notes (Textual) [Abstract]
Interest rate on convertible notes					2.75%
Principal amount of senior convertible notes	402,500,000		402,500,000		402,500,000		402,500,000
Net proceeds of unsecured senior convertible notes					359,200,000
Debt instrument, maturity date					Jul. 01, 2017
Initial conversion rate adjustment Shares					23.7344
Base principal amount per note					1,000
Initial conversion price of convertible notes					$ 42.13
Business day period						5 days
Fair value of debt conversion cost						88,900,000
Debt discount, interest rate						8.00%
Contractual Coupon Interest Expense	2,800,000	2,800,000	5,500,000	5,500,000
Amortization of Debt Discount (Premium)	3,600,000	3,400,000	7,200,000	6,700,000
Number of common stock to be purchased						9,553,096
Initial stock price at which shares to be purchased						$ 42.13
Cost of hedge transaction						80,100,000
Number of warrants to be acquired						477,654
Initial strike price at which Warrants to be acquired						988.51
Number of common stock shares preferred stock convertible into						20
Number Of Securities Called By Warrant Transaction						9,553,080
Cash proceeds from the sale of warrants						$ 47,900,000
Minimum [Member] | 2.75% Senior Convertible Notes due 2017 [Member]
Senior Convertible Notes (Textual) [Abstract]
Consecutive trading days immediately preceding calendar quarter						20 days
Percentage of conversion price						130.00%
Maximum [Member] | 2.75% Senior Convertible Notes due 2017 [Member]
Senior Convertible Notes (Textual) [Abstract]
Consecutive trading days immediately preceding calendar quarter						30 days
Percentage of conversion price						98.00%