Selected Quarterly Financial Data (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2015	Sep. 30, 2015	Jun. 30, 2015	Mar. 31, 2015	Dec. 31, 2014	Sep. 30, 2014	Jun. 30, 2014	Mar. 31, 2014	Dec. 31, 2015	Dec. 31, 2014	Dec. 31, 2013
Selected Quarterly Financial Data [Abstract]
Revenue	$ 65,692	$ 66,117	$ 59,366	$ 58,492	$ 58,810	$ 59,203	$ 55,312	$ 54,264	$ 249,667	$ 227,589	$ 212,405
Operating expenses	68,292	42,861	36,232	34,842	31,595	31,954	30,815	29,671	182,227	124,035	103,638
Operating (loss) income	(2,600)	23,256	23,134	23,650	27,215	27,249	24,497	24,593	67,440	103,554	108,767
Net (loss) income attributable to CAI common stockholders	$ (12,582)	$ 12,989	$ 12,889	$ 13,542	$ 16,162	$ 16,395	$ 13,446	$ 14,271	$ 26,838	$ 60,274	$ 63,926
Net (loss) income per basic share attributable to CAI common stockholders	$ (0.62)	$ 0.62	$ 0.61	$ 0.65	$ 0.78	$ 0.78	$ 0.61	$ 0.64	$ 1.29	$ 2.91	$ 2.89
Net (loss) income per diluted share attributable to CAI common stockholders	$ (0.62)	$ 0.62	$ 0.60	$ 0.64	$ 0.76	$ 0.77	$ 0.60	$ 0.63	$ 1.28	$ 2.85	$ 2.82