Borrowings - Convertible Senior Notes (Details) (USD $)	0 Months Ended	3 Months Ended
	Aug. 13, 2013	Mar. 31, 2015	Dec. 31, 2014
Debt Instrument [Line Items]
Minimum average share price triggering dilutive effect (usd per share)		$ 65.72
Convertible debt, estimated fair value		$ 310,230,000	$ 324,757,000
Convertible Senior Notes [Member]
Debt Instrument [Line Items]
Face amount	287,500,000.000	287,500,000	287,500,000
Stated percentage	3.00%	3.00%
Redemption price	100.00%
Conversion ratio	15.2172
Minimum average share price triggering dilutive effect (usd per share)	$ 65.72	$ 65.72
Convertible debt, estimated fair value	255,300,000
Carrying amount of convertible debt	32,200,000	31,306,000	31,306,000
Debt Issuance Cost	7,300,000
Equity and debt issuance costs	8,200,000
Equity Issuance Costs	$ 900,000
Interest rate at period end		4.92%