Consolidated Statement of Shareholders' Equity - USD ($) $ in Thousands	Total	Common Stock and paid-in capital	Retained earnings	Treasury stock	Shares issued
Balance, beginning of period at Dec. 31, 2018		$ 426,737	$ 422,235	$ (135,576)
Balance, beginning of period (in shares) at Dec. 31, 2018				13,663,194	98,924,501
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Exercise of stock options		23,139
Stock-based compensation expense		10,979
Vesting of restricted stock units, net of shares withheld for employee tax		(6,768)
Net income	$ 19,642		19,642
Exercise of stock options (in shares)	1,443,685				1,443,685
Vesting of restricted stock units, net of shares withheld for employee tax (in shares)					376,891
Balance, end of period at Mar. 31, 2019	$ 760,388	454,087	441,877	$ (135,576)
Balance, end of period (in shares) at Mar. 31, 2019				13,663,194	100,745,077
Balance, beginning of period at Dec. 31, 2019	854,865	480,982	509,459	$ (135,576)
Balance, beginning of period (in shares) at Dec. 31, 2019				13,663,194	101,766,468
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Exercise of stock options		125
Stock-based compensation expense		13,510
Vesting of restricted stock units, net of shares withheld for employee tax		(3,335)
Net income	$ 12,682		12,682
Exercise of stock options (in shares)	13,561				13,561
Vesting of restricted stock units, net of shares withheld for employee tax (in shares)					293,498
Balance, end of period at Mar. 31, 2020	$ 877,847	$ 491,282	$ 522,141	$ (135,576)
Balance, end of period (in shares) at Mar. 31, 2020				13,663,194	102,073,527