CONSOLIDATED BALANCE SHEETS (Parenthetical) - USD ($) $ in Thousands	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
CONSOLIDATED BALANCE SHEETS
Allowance for doubtful accounts	$ 15,521	$ 14,418	$ 15,241	$ 16,296	$ 15,027	$ 14,419	$ 14,033	$ 13,225	$ 9,944	$ 6,472
Common stock, par value (in dollars per share)	$ 0.01	$ 0.01	$ 0.01	$ 0.01	$ 0.01	$ 0.01	$ 0.01	$ 0.01
Common stock, shares authorized	60,000,000	60,000,000	60,000,000	60,000,000	60,000,000	60,000,000	60,000,000	60,000,000
Common stock, shares issued	36,183,894	36,158,347	36,144,560	36,044,247	35,854,106	35,825,040	35,816,784	35,765,547
Common stock, shares outstanding	36,041,073	36,015,526	36,001,739	35,901,426	35,711,285	35,682,219	35,673,963	35,622,726
Treasury stock, shares	142,821	142,821	142,821	142,821	142,821	142,821	142,821	141,154