Selected Quarterly Financial Data (Details) - USD ($) $ / shares in Units, $ in Thousands	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
Selected Quarterly Financial Data [Abstract]
Revenue	$ 115,567	$ 115,452	$ 105,705	$ 95,374	$ 94,034	$ 90,161	$ 82,692	$ 81,506	$ 432,098	$ 348,393	$ 294,354
Operating expenses	72,578	72,571	65,786	60,658	57,631	58,267	57,924	63,555	271,593	237,377	241,068
Operating (loss) income	42,989	42,881	39,919	34,716	36,403	31,894	24,768	17,951	160,505	111,016	53,286
Net (loss) income attributable to CAI common stockholders	$ 17,200	$ 20,006	$ 19,149	$ 17,117	$ 36,563	$ 17,587	$ 12,638	$ 5,272	$ 73,472	$ 72,060	$ 5,997
Net (loss) income per basic share attributable to CAI common stockholders	$ 0.90	$ 1.04	$ 0.98	$ 0.84	$ 1.86	$ 0.92	$ 0.66	$ 0.28	$ 3.76	$ 3.74	$ 0.31
Net (loss) income per diluted share attributable to CAI common stockholders	$ 0.89	$ 1.03	$ 0.97	$ 0.83	$ 1.81	$ 0.90	$ 0.65	$ 0.27	$ 3.71	$ 3.68	$ 0.31