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, 2017	$ 676,334	$ 353,392	$ 321,408	$ 1,534
Beginning balance (in shares) at Dec. 31, 2017		50,248
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	5,269		5,269
Other comprehensive income/loss	4,072			4,072
Stock-based compensation expense	1,256	$ 1,256
Options exercised	1,286	$ 1,286
Options exercised (in shares)		91
Issuance of common stock under Employee Stock Purchase Plan	294	$ 294
Issuance of common stock under Employee Stock Purchase Plans (in shares)		7
Ending balance at Mar. 31, 2018	688,511	$ 356,228	326,677	5,606
Ending balance (in shares) at Mar. 31, 2018		50,346
Beginning balance at Dec. 31, 2017	676,334	$ 353,392	321,408	1,534
Beginning balance (in shares) at Dec. 31, 2017		50,248
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	16,210
Other comprehensive income/loss	532
Shares surrendered in exchange for exercise of stock options	$ (1,684)
Shares surrendered in exchange for exercise of stock options (in shares)	(32)
Ending balance at Jun. 30, 2018	$ 699,254	$ 359,570	337,618	2,066
Ending balance (in shares) at Jun. 30, 2018		50,635
Beginning balance at Mar. 31, 2018	688,511	$ 356,228	326,677	5,606
Beginning balance (in shares) at Mar. 31, 2018		50,346
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	10,941		10,941
Other comprehensive income/loss	(3,540)			(3,540)
Stock-based compensation expense	1,565	$ 1,565
Options exercised	5,307	$ 5,307
Options exercised (in shares)		357
Issuance of common stock under Employee Stock Purchase Plan	220	$ 220
Issuance of common stock under Employee Stock Purchase Plans (in shares)		4
Shares surrendered in exchange for payment of payroll tax liabilities	(2,065)	$ (2,065)
Shares surrendered in exchange for payment of payroll tax liabilities (in shares)		(40)
Shares surrendered in exchange for exercise of stock options	(1,685)	$ (1,685)
Shares surrendered in exchange for exercise of stock options (in shares)		(32)
Ending balance at Jun. 30, 2018	699,254	$ 359,570	337,618	2,066
Ending balance (in shares) at Jun. 30, 2018		50,635
Beginning balance at Dec. 31, 2018	$ 932,775	$ 571,383	363,425	(2,033)
Beginning balance (in shares) at Dec. 31, 2018	54,893	54,893
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	$ 6,195		6,195
Other comprehensive income/loss	(2,515)			(2,515)
Stock-based compensation expense	1,766	$ 1,766
Options exercised	1,365	$ 1,365
Options exercised (in shares)		95
Issuance of common stock under Employee Stock Purchase Plan	432	$ 432
Issuance of common stock under Employee Stock Purchase Plans (in shares)		7
Ending balance at Mar. 31, 2019	940,111	$ 574,946	369,713	(4,548)
Ending balance (in shares) at Mar. 31, 2019		54,995
Beginning balance at Dec. 31, 2018	$ 932,775	$ 571,383	363,425	(2,033)
Beginning balance (in shares) at Dec. 31, 2018	54,893	54,893
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	$ 13,054
Other comprehensive income/loss	(3,114)
Shares surrendered in exchange for exercise of stock options	$ 0
Shares surrendered in exchange for exercise of stock options (in shares)	0
Ending balance at Jun. 30, 2019	$ 950,675	$ 579,250	376,572	(5,147)
Ending balance (in shares) at Jun. 30, 2019	55,079	55,079
Beginning balance at Mar. 31, 2019	$ 940,111	$ 574,946	369,713	(4,548)
Beginning balance (in shares) at Mar. 31, 2019		54,995
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Net income	6,859		6,859
Other comprehensive income/loss	(599)			(599)
Stock-based compensation expense	2,523	$ 2,523
Options exercised	1,441	$ 1,441
Options exercised (in shares)		78
Issuance of common stock under Employee Stock Purchase Plan	340	$ 340
Issuance of common stock under Employee Stock Purchase Plans (in shares)		6
Ending balance at Jun. 30, 2019	$ 950,675	$ 579,250	$ 376,572	$ (5,147)
Ending balance (in shares) at Jun. 30, 2019	55,079	55,079