Quarterly Results (Unaudited) (Details) - USD ($)	3 Months Ended																12 Months Ended
	Dec. 31, 2019		Sep. 30, 2019		Jun. 30, 2019		Mar. 31, 2019		Dec. 31, 2018		Sep. 30, 2018		Jun. 30, 2018		Mar. 31, 2018		Dec. 31, 2019		Dec. 31, 2018		Dec. 31, 2017
Quarterly Financial Information Disclosure [Abstract]
Total revenues	$ 628,383,000		$ 624,474,000		$ 635,037,000		$ 614,576,000		$ 587,044,000		$ 595,962,000		$ 585,890,000		$ 607,221,000		$ 2,502,470,000		$ 2,376,117,000		$ 2,018,197,000
Gross profit	177,438,000		196,404,000		191,214,000		187,263,000		176,790,000		197,097,000		176,577,000		179,855,000		752,319,000		730,319,000		676,751,000
Net Income (Loss) Attributable to Parent	$ 14,620,000		$ 16,847,000		$ 19,446,000		$ (1,907,000)		$ 23,877,000		$ 19,882,000		$ 2,657,000		$ (145,666,000)		$ 49,006,000		$ (99,250,000)		$ 57,298,000
Earnings (loss) per common share - Basic (in dollars per share)	$ 0.37	[1]	$ 0.43	[1]	$ 0.49	[1]	$ (0.05)	[1]	$ 0.61	[1]	$ 0.51	[1]	$ 0.07	[1]	$ (3.74)	[1]	$ 1.24	[1]	$ (2.53)	[1]	$ 1.48
Earnings (loss) per common share - Diluted (in dollars per share)	$ 0.36	[1]	$ 0.42	[1]	$ 0.49	[1]	$ (0.05)	[1]	$ 0.60	[1]	$ 0.50	[1]	$ 0.07	[1]	$ (3.74)	[1]	$ 1.23	[1]	$ (2.53)	[1]	$ 1.45

[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.