Convertible Senior Notes - Additional Information (Detail) - USD ($) $ / shares in Units, $ in Thousands	1 Months Ended				3 Months Ended			6 Months Ended		12 Months Ended
	Jun. 30, 2017	Jan. 31, 2016	Jun. 30, 2014	Jul. 31, 2013	Jun. 30, 2017	Mar. 31, 2017	Jun. 30, 2016	Jun. 30, 2017	Jun. 30, 2016	Dec. 31, 2016
Debt Instrument [Line Items]
Long term debt, face amount	$ 155,728				$ 155,728			$ 155,728		$ 206,865
Gain recognized on retirement of debt								114	$ 69
Payment for repurchase of convertible notes								35,614	2,626
Amortization of debt issuance costs recognized as interest expense					800		$ 500	1,100	$ 1,100
4.875% Convertible Senior Notes (due 2020)
Debt Instrument [Line Items]
Long term debt, face amount	$ 113,000		$ 115,000		$ 113,000			$ 113,000		$ 113,000
Debt instrument, interest rate	4.875%		4.875%		4.875%			4.875%		4.875%
Debt instrument, maturity date			Jun. 01, 2020
Frequency of interest payment								Semi-annually
Conversion rate in share per $1000 principal amount of notes			103.7613
Debt instrument, conversion rate			$ 9.64
Debt instrument repurchase amount		$ 2,000
Write-off of debt issuance costs		100
Gain recognized on retirement of debt		$ 100
Convertible senior note payable, fair value	$ 98,000				$ 98,000			$ 98,000		$ 89,300
Debt instrument, maturity year								2020		2020
4.25% Convertible Senior Notes (due 2018)
Debt Instrument [Line Items]
Long term debt, face amount	$ 42,728			$ 100,000	$ 42,728			$ 42,728		$ 93,865
Debt instrument, interest rate	4.25%			4.25%	4.25%			4.25%		4.25%
Debt instrument, maturity date				Aug. 01, 2018
Frequency of interest payment								Semi-annually
Conversion rate in share per $1000 principal amount of notes				114.3674
Debt instrument, conversion rate				$ 8.74
Debt instrument repurchase amount	$ 12,000				$ 12,000	$ 39,100		$ 12,000		$ 6,100
Write-off of debt issuance costs					100					100
Gain recognized on retirement of debt					100
Payment for repurchase of convertible notes					11,600	24,100
Convertible senior note payable, fair value	42,100				42,100			$ 42,100		$ 83,700
Debt instrument, maturity year								2018		2018
4.25% Convertible Senior Notes (due 2018) | Common Stock
Debt Instrument [Line Items]
Debt instrument repurchase amount	$ 11,600				$ 11,600	$ 39,100		$ 11,600
Debt instrument shares common stock issued upon conversion	112,400				112,400	2,865,000