Convertible Senior Notes - Additional Information (Details)			1 Months Ended			5 Months Ended	12 Months Ended
	Dec. 23, 2013 USD ($)	Dec. 17, 2013 USD ($) shares	Oct. 31, 2017 USD ($) shares	Jul. 31, 2017 shares	Dec. 31, 2016 USD ($) open_market_purchase shares	Dec. 31, 2017 USD ($) $ / shares shares	Dec. 31, 2017 USD ($) day $ / shares shares	Dec. 31, 2016 USD ($) shares	Dec. 31, 2015 USD ($)
Debt Instrument [Line Items]
Payments for repurchase							$ 27,500,000	$ 9,014,000	$ 0
Stock issued (shares) | shares				3,243,882		10,314,250		10,890,915
2018 Convertible Notes [Member]
Debt Instrument [Line Items]
Debt instrument face value					$ 101,800,000	$ 74,300,000	$ 74,300,000	$ 101,800,000
2.75% Convertible Senior Notes Due 2018 [Member]
Debt Instrument [Line Items]
Sale of convertible notes, principal amount		$ 120,000,000
Interest rate		2.75%					2.75%
Common shares converted value (shares) | shares		120,000	69,472		9,963		11,400,000.0
Conversion rate (shares) | shares							95
Conversion rate, price per $1,000 | $ / shares						$ 1,000	$ 1,000
Money conversion price per share ($ per share) | $ / shares						$ 10.53	$ 10.53
Net proceeds from convertible notes	$ 115,400,000
Professional fee	4,600,000
Additional paid-in capital	$ 13,100,000
Number Of open market purchases | open_market_purchase					2
Repurchase of principal			$ 69,500,000		$ 10,000,000
Payments for repurchase			$ 27,300,000		9,000,000
Loss on 2018 Convertible Note purchase							$ 800,000	25,000
Debt instrument face value					$ 110,000,000	$ 40,600,000	40,600,000	110,000,000
Proceeds from unwinding							$ 5,800,000	$ 21,000
Stock issued (shares) | shares			5,400,000
Common stock issued, value			$ 73,000,000
Strike price per share ($ per share) | $ / shares						$ 14.03	$ 14.03
Threshold percentage of conversion price							130.00%
Convertible senior notes trading price						$ 1,000	$ 1,000
Percentage of product of last reported sale price of common stock							98.00%
2.75% Convertible Senior Notes Due 2018 [Member] | Minimum [Member]
Debt Instrument [Line Items]
Debt convertible trading days							20 days
Debt convertible consecutive trading days | day							5
2.75% Convertible Senior Notes Due 2018 [Member] | Maximum [Member]
Debt Instrument [Line Items]
Debt convertible consecutive trading days | day							30