Stockholders' Equity (Details) - USD ($)	1 Months Ended	3 Months Ended		6 Months Ended
	Jun. 30, 2015	Jun. 30, 2015	Jun. 30, 2014	Jun. 30, 2015	Jun. 30, 2014	Feb. 25, 2015
Class of Stock [Line Items]
Increase in stockholders' equity				$ 452,700,000
Net income		$ 38,943,000	$ 7,811,000	67,096,000	$ 12,309,000
Income tax benefit related to share-based compensation				13,200,000
Proceeds from common stock offering, net of issuance costs	$ 373,200,000			$ 373,151,000	$ 0
Warrants issued				13,490,236
Warrant, strike price per share	$ 53.8475	$ 53.8475		$ 53.8475
Trading days measurement period				160 days
Stated percentage of warrants	1.125%	1.125%		1.125%
Common Stock
Class of Stock [Line Items]
Number of shares issued in connection with an underwritten public offering	5,750,000
Share price in the offering (dollars per share)	$ 64.90	$ 64.90		$ 64.90
Number of common stock issued				460,000
February 2015 Repurchase Program | Common Stock
Class of Stock [Line Items]
Authorized repurchase amount						$ 50,000,000