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		26,998
Stock-based compensation expense		15,781
Vesting of restricted stock units, net of shares withheld for employee tax		(6,947)
Net income	$ 48,742		48,742
Exercise of stock options (in shares)	1,686,408				1,686,408
Vesting of restricted stock units, net of shares withheld for employee tax (in shares)					403,497
Balance, end of period at Jun. 30, 2019	$ 797,970	462,569	470,977	$ (135,576)
Balance, end of period (in shares) at Jun. 30, 2019				13,663,194	101,014,406
Balance, beginning of period at Mar. 31, 2019		454,087	441,877	$ (135,576)
Balance, beginning of period (in shares) at Mar. 31, 2019				13,663,194	100,745,077
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Exercise of stock options		3,859
Stock-based compensation expense		4,802
Vesting of restricted stock units, net of shares withheld for employee tax		(179)
Net income	$ 29,100		29,100
Exercise of stock options (in shares)	242,723				242,723
Vesting of restricted stock units, net of shares withheld for employee tax (in shares)					26,606
Balance, end of period at Jun. 30, 2019	$ 797,970	462,569	470,977	$ (135,576)
Balance, end of period (in shares) at Jun. 30, 2019				13,663,194	101,014,406
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		1,619
Stock-based compensation expense		17,950
Vesting of restricted stock units, net of shares withheld for employee tax		(3,460)
Net income	$ 19,295		19,295
Exercise of stock options (in shares)	91,589				91,589
Vesting of restricted stock units, net of shares withheld for employee tax (in shares)					315,097
Balance, end of period at Jun. 30, 2020	$ 890,269	497,091	528,754	$ (135,576)
Balance, end of period (in shares) at Jun. 30, 2020				13,663,194	102,173,154
Balance, beginning of period at Mar. 31, 2020		491,282	522,141	$ (135,576)
Balance, beginning of period (in shares) at Mar. 31, 2020				13,663,194	102,073,527
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Exercise of stock options		1,494
Stock-based compensation expense		4,440
Vesting of restricted stock units, net of shares withheld for employee tax		(125)
Net income	$ 6,613		6,613
Exercise of stock options (in shares)	78,028				78,028
Vesting of restricted stock units, net of shares withheld for employee tax (in shares)					21,599
Balance, end of period at Jun. 30, 2020	$ 890,269	$ 497,091	$ 528,754	$ (135,576)
Balance, end of period (in shares) at Jun. 30, 2020				13,663,194	102,173,154