Description of the business and recent developments: Stockholders' deficit (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2020	Sep. 30, 2019	Sep. 30, 2020	Sep. 30, 2019
Increase (Decrease) in Stockholders' Equity
Balance	$ (235,550)	$ (176,590)	$ (203,679)	$ (149,002)
Balance (in shares)			46,840,434
Equity-based compensation	7,147	5,311	$ 19,371	14,796
Foreign currency translation	5,408	(4,709)	4,828	(4,748)
Issuances of common stock				1
Exercises of options	185	351	1,174	1,269
Common stock purchases and retirement	(269)		(269)
Dividends paid	(32,657)	(28,565)	(94,952)	(82,871)
Net (loss) income	(4,955)	13,701	12,836	30,054
Balance	$ (260,691)	(190,501)	$ (260,691)	(190,501)
Balance (in shares)	47,284,336		47,284,336
Common Stock
Increase (Decrease) in Stockholders' Equity
Balance	$ 47	$ 47	$ 47	$ 46
Balance (in shares)	47,279,201	46,806,370	46,840,434	46,336,499
Forfeitures of shares granted to employees (in shares)	(4,932)	(4,508)	(42,212)	(8,394)
Issuances of common stock				$ 1
Issuances of common stock (in shares)	10,500	10,572	465,530	459,550
Exercises of options (in shares)	4,134	9,152	25,151	33,931
Common stock purchases and retirement (in shares)	(4,567)		(4,567)
Balance	$ 47	$ 47	$ 47	$ 47
Balance (in shares)	47,284,336	46,821,586	47,284,336	46,821,586
Additional Paid-in Capital
Increase (Decrease) in Stockholders' Equity
Balance	$ 506,391	$ 481,734	$ 493,178	$ 471,331
Equity-based compensation	7,147	5,311	19,371	14,796
Exercises of options	185	351	1,174	1,269
Common stock purchases and retirement	(269)		(269)
Balance	513,454	487,396	513,454	487,396
Accumulated Other Comprehensive Income (Loss)
Increase (Decrease) in Stockholders' Equity
Balance	(12,906)	(10,967)	(12,326)	(10,928)
Foreign currency translation	5,408	(4,709)	4,828	(4,748)
Balance	(7,498)	(15,676)	(7,498)	(15,676)
Accumulated Deficit
Increase (Decrease) in Stockholders' Equity
Balance	(729,082)	(647,404)	(684,578)	(609,451)
Dividends paid	(32,657)	(28,565)	(94,952)	(82,871)
Net (loss) income	(4,955)	13,701	12,836	30,054
Balance	$ (766,694)	$ (662,268)	$ (766,694)	$ (662,268)