Stockholders' Equity - Schedule of Changes in Stockholders' Equity (Details) - USD ($) shares in Thousands, $ in Thousands		3 Months Ended		9 Months Ended
		Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Balance		$ 635,371	$ 573,130	$ 616,030	$ 566,004
Net income		16,671	13,692	42,705	35,806
Other comprehensive income		(568)	558	(2,276)	3,030
Equity compensation		3,335	2,798	8,685	8,159
Exercise of stock options		2,309	2,291	5,842	4,722
Net payments for stock issuances and buybacks		(3,802)	(7,683)	(12,399)	(32,935)
Dividends declared		(2,643)		(7,914)
Balance		650,673	584,786	650,673	584,786
Common Stock
Balance		$ 22	$ 22	$ 22	$ 22
Balance (in shares)		18,826	18,718	18,662	19,021
Exercise of stock options (in shares)		85	82	210	176
Issuance of shares pursuant to vesting of restricted stock units		8	11	198	181
Net payments for stock issuances and buybacks (in shares)		(51)	(172)	(202)	(739)
Balance		$ 22	$ 22	$ 22	$ 22
Balance (in shares)		18,868	18,639	18,868	18,639
Additional Paid-in Capital
Balance		$ 317,013	$ 300,394	$ 307,821	$ 292,427
Equity compensation		3,292	2,709	8,507	7,921
Exercise of stock options		2,309	2,291	5,842	4,722
Net payments for stock issuances and buybacks		(14)		430	324
Balance		322,600	305,394	322,600	305,394
Retained Earnings
Balance		456,358	394,004	434,766	371,890
Net income		16,671	13,692	42,705	35,806
Reclassification of stranded tax effects due to adoption of accounting principle				829
Dividends declared		(2,643)		(7,914)
Balance		470,386	407,696	470,386	407,696
Treasury Stock
Balance		$ (130,446)	$ (114,122)	$ (121,540)	$ (88,695)
Balance (in shares)		3,502	3,202	3,357	2,642
Equity compensation		$ 43	$ 89	$ 178	$ 238
Issuance of shares pursuant to vesting of restricted stock units		(1)	(4)	(7)	(11)
Net payments for stock issuances and buybacks		$ (3,788)	$ (7,683)	$ (12,829)	$ (33,259)
Net payments for stock issuances and buybacks (in shares)		51	172	202	739
Balance		$ (134,191)	$ (121,716)	$ (134,191)	$ (121,716)
Balance (in shares)		3,552	3,370	3,552	3,370
Accumulated Other Comprehensive Loss
Balance		$ (7,576)	$ (7,168)	$ (5,039)	$ (9,640)
Other comprehensive income		(568)	558	(2,276)	3,030
Reclassification of stranded tax effects due to adoption of accounting principle	[1]			(829)
Balance		$ (8,144)	$ (6,610)	$ (8,144)	$ (6,610)

[1] The Company has adjusted the balance at December 31, 2017 of accumulated other comprehensive loss for the stranded tax effects caused by the enactment of the Tax Act.