Description of the business and recent developments: Stockholders' deficit (Details) - USD ($) $ in Thousands	3 Months Ended		6 Months Ended
	Jun. 30, 2021	Jun. 30, 2020	Jun. 30, 2021	Jun. 30, 2020
Increase (Decrease) in Stockholders' Equity
Balance	$ (307,559)	$ (222,225)	$ (293,166)	$ (203,679)
Balance (in shares)			47,214,077
Equity-based compensation	8,476	6,666	$ 16,307	12,224
Foreign currency translation	1,776	2,913	(3,434)	(580)
Issuances of common stock			1
Exercises of options	660	270	875	989
Dividends paid	(37,001)	(31,738)	(73,082)	(62,295)
Net (loss) income	(2,493)	8,564	16,358	17,791
Balance	$ (336,141)	(235,550)	$ (336,141)	(235,550)
Balance (in shares)	47,655,131		47,655,131
Common Stock
Increase (Decrease) in Stockholders' Equity
Balance	$ 48	$ 47	$ 47	$ 47
Balance (in shares)	47,522,672	47,139,369	47,214,077	46,840,434
Forfeitures of shares granted to employees (in shares)	(5,626)	(972)	(25,302)	(37,280)
Issuances of common stock			$ 1
Issuances of common stock (in shares)	125,060	135,280	448,760	455,030
Exercises of options (in shares)	13,025	5,524	17,596	21,017
Balance	$ 48	$ 47	$ 48	$ 47
Balance (in shares)	47,655,131	47,279,201	47,655,131	47,279,201
Additional Paid-in Capital
Increase (Decrease) in Stockholders' Equity
Balance	$ 523,913	$ 499,455	$ 515,867	$ 493,178
Equity-based compensation	8,476	6,666	16,307	12,224
Exercises of options	660	270	875	989
Balance	533,049	506,391	533,049	506,391
Accumulated Other Comprehensive Income (Loss)
Increase (Decrease) in Stockholders' Equity
Balance	(6,516)	(15,819)	(1,306)	(12,326)
Foreign currency translation	1,776	2,913	(3,434)	(580)
Balance	(4,740)	(12,906)	(4,740)	(12,906)
Accumulated Deficit
Increase (Decrease) in Stockholders' Equity
Balance	(825,004)	(705,908)	(807,774)	(684,578)
Dividends paid	(37,001)	(31,738)	(73,082)	(62,295)
Net (loss) income	(2,493)	8,564	16,358	17,791
Balance	$ (864,498)	$ (729,082)	$ (864,498)	$ (729,082)