Convertible Senior Notes Narrative (Details) (USD $)	6 Months Ended		1 Months Ended
	Jun. 30, 2014 D	Dec. 31, 2013	Jun. 30, 2012 Convertible Debt [Member]
Debt Instrument [Line Items]
Senior notes	$ 241,304,000	$ 236,088,000	$ 275,000,000
Interest rate			1.375%
Proceeds from offering			266,200,000
Trading period	20
Consecutive trading period	30 days
Percent of conversion price	130.00%
Measurement period	5 days
Principal amount in covenant	$ 1,000
Percent of trading price	98.00%
Conversion ratio	0.358038
Conversion price	$ 27.93
Percent of principal amount plus accrued and unpaid interest	100.00%
Percent of principal amount	25.00%
Percent of principal amount, plus accrued and unpaid interest, due and payable	100.00%
Percent of principal amount, plus accrued and unpaid interest, due and payable if bankruptcy, insolvency or reorganization occurs	100.00%
Initial discount amortization period	5 years