Quarterly Results (Unaudited) (Details) - USD ($)	3 Months Ended																12 Months Ended
	Dec. 31, 2018		Sep. 30, 2018		Jun. 30, 2018		Mar. 31, 2018		Dec. 31, 2017		Sep. 30, 2017		Jun. 30, 2017		Mar. 31, 2017		Dec. 31, 2018		Dec. 31, 2017		Dec. 31, 2016
Quarterly Financial Information Disclosure [Abstract]
Total revenues	$ 587,044,000		$ 595,962,000		$ 585,890,000		$ 607,221,000		$ 550,776,000		$ 486,747,000		$ 503,082,000		$ 477,592,000		$ 2,376,117,000		$ 2,018,197,000		$ 2,013,186,000
Gross profit	176,790,000		197,097,000		176,577,000		179,855,000		175,082,000		165,755,000		178,277,000		157,637,000		730,319,000		676,751,000		662,532,000
Net Income (Loss) Attributable to Parent	$ 23,877,000		$ 19,882,000		$ 2,657,000		$ (145,666,000)		$ 1,780,000		$ 25,576,000		$ 14,097,000		$ 15,845,000		$ (99,250,000)		$ 57,298,000		$ 31,770,000
Earnings (loss) per common share - Basic (in dollars per share)	$ 0.61	[1]	$ 0.51	[1]	$ 0.07	[1]	$ (3.74)	[1]	$ 0.05	[1]	$ 0.66	[1]	$ 0.36	[1]	$ 0.41	[1]	$ (2.53)	[1]	$ 1.48	[1]	$ 0.83
Earnings (loss) per common share - Diluted (in dollars per share)	$ 0.60	[1]	$ 0.50	[1]	$ 0.07	[1]	$ (3.74)	[1]	$ 0.05	[1]	$ 0.65	[1]	$ 0.36	[1]	$ 0.40	[1]	$ (2.53)	[1]	$ 1.45	[1]	$ 0.82

[1] The sum of the quarterly EPS data presented in the table may not equal the annual results due to rounding and the impact of dilutive securities on the annual versus the quarterly EPS calculations.