Long-term debt: (Details) (USD $)			0 Months Ended		12 Months Ended								1 Months Ended	3 Months Ended	12 Months Ended
	Dec. 31, 2013	Dec. 31, 2012	Aug. 19, 2013 Senior Notes	Jan. 26, 2011 Senior Notes	Dec. 31, 2013 Senior Notes	Dec. 31, 2012 Senior Notes	Dec. 31, 2011 Senior Notes	Dec. 31, 2013 Senior Notes Prior to February 15, 2015	Dec. 31, 2013 Senior Notes 12-month period beginning on February 15, 2015	Dec. 31, 2013 Senior Notes 12-month period beginning on February 15, 2016	Dec. 31, 2013 Senior Notes 12-month period beginning on February 15, 2017 and thereafter	Dec. 31, 2013 Senior Notes Prior to February 15, 2014	Jun. 30, 2007 Convertible senior notes	Dec. 31, 2013 Convertible senior notes	Dec. 31, 2013 Convertible senior notes D	Dec. 31, 2012 Convertible senior notes	Dec. 31, 2011 Convertible senior notes	Dec. 31, 2008 Convertible senior notes	Dec. 31, 2013 Convertible senior notes June 15, 2014, 2017 and 2022	Dec. 31, 2013 Convertible senior notes After June 20, 2014
Long-term debt
Interest rate (as a percent)			8.375%	8.375%									1.00%	1.00%	1.00%	1.00%
Aggregate principal amount of debt issued			$ 65,000,000	$ 175,000,000	$ 240,000,000								$ 200,000,000	$ 92,000,000	$ 92,000,000
Proceeds from issuance of long-term debt, net of issuance costs			69,900,000	170,500,000									195,100,000
Debt issuance costs			1,000,000	4,500,000
Premium price of debt instrument (as a percent)			109.00%
Senior secured notes, premium (in dollars)	5,423,000	0	5,900,000
Security of senior notes and guarantees, expressed as a percentage of equity interests of first-tier foreign subsidiaries held by Company and its guarantors					65.00%
Percentage of principal amount that the holders of the Convertible Notes may require the Company to repurchase								100.00%	104.118%	102.094%	100.00%	108.375%							100.00%	100.00%
Percentage of outstanding principal amount used in calculation of make-whole premium								1.00%
Discount rate used to compute make-whole premium, description of variable interest rate					Treasury Rate
Discount rate used to compute make-whole premium, basis points added to reference rate (as a percent)					0.50%
Maximum percentage of principal amount of debt instrument which the entity may redeem with proceeds from certain equity offerings												35.00%
Percentage of principal amount at which notes will be required to be repurchased in the event of a change of control					101.00%
Minimum amount of proceeds from certain asset sales at which company must offer to purchase notes					20,000,000
Percentage of principal amount at which notes will be required to be repurchased upon meeting minimum proceeds from certain asset sales					100.00%
Minimum percentage of principal amount of debt instrument at which holder may declare unpaid principal and accrued interest to be due and payable					25.00%
Percentage of original issuance discount													2.25%
Aggregate face value of debt purchased																		108,000,000
Purchase of convertible notes in cash																		48,600,000
Initial conversion price of notes (in dollars per share)														$ 47.52	$ 47.52
Conversion ratio, number of shares per $1,000 principal amount															0.021043
Number of days within 30 consecutive trading days in which the closing price of the entity's common stock must exceed the conversion price for the notes to be redeemable															20
Number of consecutive trading days during which the closing price of the entity's common stock must exceed the conversion price for at least 20 days in order to make the notes redeemable															30 days
Percentage of the closing sales price of the entity's common stock that the conversion price must exceed in order to make the notes convertible															130.00%
Conversion ratio minimum, number of shares per $1,000 principal amount															0.0368251
Special interest rate required to be paid for first 90 days after failure to maintain shelf registration statement with SEC (as a percent)															0.25%
Initial period to charge special interest after failure to maintain shelf registration statement with SEC															90 days
Special interest rate required to be paid after the first 90 day period after failure to maintain shelf registration statement with SEC (as a percent)															0.50%
Additional interest rate in the event of default (as a percent)															0.25%
Debt and equity components for the Convertible Notes
Principal amount														91,978,000	91,978,000	91,978,000
Unamortized discount	(3,099,000)	(9,494,000)												(3,099,000)	(3,099,000)	(9,494,000)
Net carrying amount														88,879,000	88,879,000	82,484,000
Additional paid-in capital														74,933,000	74,933,000	74,933,000
Amount of interest expense recognized and effective interest rate
Remaining recognition period of unamortized discount															6 months
Contractual coupon interest															920,000	920,000	920,000
Amortization of discount and costs															6,409,000	5,886,000	5,405,000
Interest expense					16,800,000	15,200,000	14,000,000							1,200,000	7,329,000	6,806,000	6,325,000
Effective interest rate (as a percent)														8.70%	8.70%	8.70%	8.70%
Long-term debt maturities
2018														240,000,000	240,000,000
Thereafter														91,978,000	91,978,000
Total														$ 331,978,000	$ 331,978,000