Description of the business and recent developments: Stockholders' deficit (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Increase (Decrease) in Stockholders' Equity
Balance	$ (336,141)	$ (235,550)	$ (293,166)	$ (203,679)
Balance (in shares)			47,214,077
Equity-based compensation	7,164	7,147	$ 23,471	19,371
Foreign currency translation	(3,818)	5,408	(7,252)	4,828
Issuances of common stock			1
Exercises of options	362	185	1,237	1,174
Common stock purchases and retirement		(269)		(269)
Dividends paid	(37,654)	(32,657)	(110,736)	(94,952)
Net income (loss)	13,320	(4,955)	29,678	12,836
Balance	$ (356,767)	(260,691)	$ (356,767)	(260,691)
Balance (in shares)	47,663,276		47,663,276
Common Stock
Increase (Decrease) in Stockholders' Equity
Balance	$ 48	$ 47	$ 47	$ 47
Balance (in shares)	47,655,131	47,279,201	47,214,077	46,840,434
Forfeitures of shares granted to employees (in shares)	(10,933)	(4,932)	(36,235)	(42,212)
Issuances of common stock			$ 1
Issuances of common stock (in shares)	11,820	10,500	460,580	465,530
Exercises of options (in shares)	7,258	4,134	24,854	25,151
Common stock purchases and retirement (in shares)		(4,567)		(4,567)
Balance	$ 48	$ 47	$ 48	$ 47
Balance (in shares)	47,663,276	47,284,336	47,663,276	47,284,336
Additional Paid-in Capital
Increase (Decrease) in Stockholders' Equity
Balance	$ 533,049	$ 506,391	$ 515,867	$ 493,178
Equity-based compensation	7,164	7,147	23,471	19,371
Exercises of options	362	185	1,237	1,174
Common stock purchases and retirement		(269)		(269)
Balance	540,575	513,454	540,575	513,454
Accumulated Other Comprehensive Income (Loss)
Increase (Decrease) in Stockholders' Equity
Balance	(4,740)	(12,906)	(1,306)	(12,326)
Foreign currency translation	(3,818)	5,408	(7,252)	4,828
Balance	(8,558)	(7,498)	(8,558)	(7,498)
Accumulated Deficit
Increase (Decrease) in Stockholders' Equity
Balance	(864,498)	(729,082)	(807,774)	(684,578)
Dividends paid	(37,654)	(32,657)	(110,736)	(94,952)
Net income (loss)	13,320	(4,955)	29,678	12,836
Balance	$ (888,832)	$ (766,694)	$ (888,832)	$ (766,694)