CONSOLIDATED STATEMENTS OF STOCKHOLDERS' EQUITY - USD ($) shares in Thousands, $ in Thousands	Total	Common Stock	Retained Earnings	Accumulated Other Comprehensive Income (Loss)
Beginning balance at Dec. 31, 2014	$ 435,259	$ 187,709	$ 249,962	$ (2,412)
Beginning balance (in shares) at Dec. 31, 2014		43,614
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	23,802		23,802
Other comprehensive income (loss)	(3,075)			(3,075)
Excess tax benefits from stock-based compensation	2,124	$ 2,124
Stock-based compensation expense	2,243	2,243
Options exercised	10,029	$ 10,029
Options exercised (in shares)		858
Issuance of common stock under Employee Stock Purchase Plans	441	$ 441
Issuance of common stock under Employee Stock Purchase Plans (in shares)		23
Shares surrendered in exchange for payment of payroll tax liabilities	(918)	$ (918)
Shares surrendered in exchange for payment of payroll tax liabilities (in shares)		(43)
Shares surrendered in exchange for exercise of stock options	(3,802)	$ (3,802)
Shares surrendered in exchange for the exercise of stock options (in shares)		(185)
Ending balance at Dec. 31, 2015	466,103	$ 197,826	273,764	(5,487)
Ending balance (in shares) at Dec. 31, 2015		44,267
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	20,121		20,121
Other comprehensive income (loss)	3,605			3,605
Excess tax benefits from stock-based compensation	669	$ 669
Stock-based compensation expense	2,506	2,506
Options exercised	4,923	$ 4,923
Options exercised (in shares)		362
Issuance of common stock under Employee Stock Purchase Plans	694	$ 694
Issuance of common stock under Employee Stock Purchase Plans (in shares)		34
Shares surrendered in exchange for payment of payroll tax liabilities	(86)	$ (86)
Shares surrendered in exchange for payment of payroll tax liabilities (in shares)		(4)
Shares surrendered in exchange for exercise of stock options	(346)	$ (346)
Shares surrendered in exchange for the exercise of stock options (in shares)		(14)
Ending balance at Dec. 31, 2016	$ 498,189	$ 206,186	293,885	(1,882)
Ending balance (in shares) at Dec. 31, 2016	44,645	44,645
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	$ 27,523		27,523
Other comprehensive income (loss)	3,416			3,416
Stock-based compensation expense	4,075	$ 4,075
Options exercised	$ 5,689	$ 5,689
Options exercised (in shares)	404	404
Issuance of common stock under Employee Stock Purchase Plans	$ 836	$ 836
Issuance of common stock under Employee Stock Purchase Plans (in shares)		24
Shares surrendered in exchange for payment of payroll tax liabilities	136,606	$ 136,606
Shares surrendered in exchange for payment of payroll tax liabilities (in shares)		5,175
Shares surrendered in exchange for exercise of stock options	0
Shares surrendered in exchange for the exercise of stock options (in shares)		0
Ending balance at Dec. 31, 2017	$ 676,334	$ 353,392	$ 321,408	$ 1,534
Ending balance (in shares) at Dec. 31, 2017	50,248	50,248