Capital Stock - Basic and Diluted Per-share Computations (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2019	Sep. 30, 2018	Sep. 30, 2019	Sep. 30, 2018	Jun. 30, 2019	Dec. 31, 2018	Jun. 30, 2018	Dec. 31, 2017
Equity [Abstract]
Net income applicable to common shareholders	$ 9,033	$ 5,020	$ 28,695	$ 21,150
Weighted average number of common shares (000's):
Issued and outstanding, beginning of period	61,290,617		61,290,617		61,331,000	61,433,589	62,522,000	64,696,000
Weighted average number of shares repurchased, net of shares issued during the period	(27,000)	29,000	(97,000)	(1,230,000)
Weighted average number of shares used in computing basic income per share	61,304,000	62,551,000	61,337,000	63,466,000
Assumed exercise of stock options and RSUs, net of shares assumed repurchased	175,000	242,000	172,000	114,000
Weighted average number of shares used in computing diluted income per share	61,479,000	62,793,000	61,509,000	63,580,000