Consolidated Statements of Stockholders' Equity - USD ($)	Total	Common Stock [Member]	Treasury Stock [Member]	Additional Paid-in Capital [Member]	Accumulated Other Comprehensive Income (Loss) [Member]	Retained Earnings [Member]
Balance at Dec. 31, 2014	$ 542,591,000	$ 64,000	$ (275,608,000)	$ 611,882,000	$ (12,084,000)	$ 218,337,000
Balance, shares at Dec. 31, 2014		63,708,000	(15,491,000)
Comprehensive income (loss)	55,869,000				(4,476,000)	60,345,000
Issuances of common stock related to business combinations	3,000,000		$ 3,000,000
Issuances of common stock related to business combinations, shares			177,000
Issuances of common stock	5,974,000			5,974,000
Issuances of common stock, shares		488,000
Tax benefits on stock options exercised and restricted stock units vested	311,000			311,000
Vesting of restricted stock and restricted stock units, net of forfeitures and tax withholdings	(1,806,000)		$ 5,000	(1,811,000)
Vesting of restricted stock and restricted stock units, net of forfeitures and tax withholdings, shares		269,000
Share-based compensation expense	10,328,000			10,328,000
Additional paid-in capital recorded through compensation expense	1,292,000			1,292,000
Repurchases of common stock	(24,021,000)		$ (24,021,000)
Repurchases of common stock, shares			(1,589,072)
Balance at Dec. 31, 2015	593,538,000	$ 64,000	$ (296,624,000)	627,976,000	(16,560,000)	278,682,000
Balance, shares at Dec. 31, 2015		64,465,000	(16,903,000)
Comprehensive income (loss)	49,452,000				(8,646,000)	58,098,000
Issuances of common stock	4,299,000			4,299,000
Issuances of common stock, shares		290,000
Tax benefits on stock options exercised and restricted stock units vested	1,218,000			1,218,000
Vesting of restricted stock and restricted stock units, net of forfeitures and tax withholdings	(3,982,000)	$ 1,000		(3,983,000)
Vesting of restricted stock and restricted stock units, net of forfeitures and tax withholdings, shares		570,000
Share-based compensation expense	13,071,000			13,071,000
Additional paid-in capital recorded through compensation expense	1,938,000			1,938,000
Repurchases of common stock	(25,057,000)		$ (25,057,000)
Repurchases of common stock, shares			(1,436,147)
Treasury stock retirement		$ (8,000)	$ 140,320,000			(140,312,000)
Treasury stock retirement, shares		(8,000,000)	8,000,000
Balance at Dec. 31, 2016	634,477,000	$ 57,000	$ (181,361,000)	644,519,000	(25,206,000)	196,468,000
Balance, shares at Dec. 31, 2016		57,325,000	(10,339,000)
Cumulative-effect adjustment resulting from the adoption of ASU 2016-09 (see Note 2)	294,000			719,000		(425,000)
Comprehensive income (loss)	80,980,000				6,028,000	74,952,000
Issuances of common stock	3,919,000	$ 1,000		3,918,000
Issuances of common stock, shares		254,000
Vesting of restricted stock and restricted stock units, net of forfeitures and tax withholdings	(4,915,000)			(4,915,000)
Vesting of restricted stock and restricted stock units, net of forfeitures and tax withholdings, shares		468,000
Share-based compensation expense	13,037,000			13,037,000
Additional paid-in capital recorded through compensation expense	2,547,000			2,547,000
Repurchases of common stock	(43,005,000)		$ (43,005,000)
Repurchases of common stock, shares			(2,322,415)
Balance at Dec. 31, 2017	$ 687,334,000	$ 58,000	$ (224,366,000)	$ 659,825,000	$ (19,178,000)	$ 270,995,000
Balance, shares at Dec. 31, 2017		58,047,000	(12,661,000)