Selected Quarterly Financial Data (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended								12 Months Ended
	Dec. 31, 2017	Sep. 30, 2017	Jun. 30, 2017	Mar. 31, 2017	Dec. 31, 2016	Sep. 30, 2016	Jun. 30, 2016	Mar. 31, 2016	Dec. 31, 2017	Dec. 31, 2016	Dec. 31, 2015
Selected Quarterly Financial Data [Abstract]
Revenue	$ 94,034	$ 90,161	$ 82,692	$ 81,506	$ 77,274	$ 78,472	$ 71,642	$ 66,966	$ 348,393	$ 294,354	$ 249,667
Operating expenses	57,631	58,267	57,924	63,555	64,664	71,110	56,784	48,510	237,377	241,068	182,227
Operating (loss) income	36,403	31,894	24,768	17,951	12,610	7,362	14,858	18,456	111,016	53,286	67,440
Net (loss) income attributable to CAI common stockholders	$ 36,563	$ 17,587	$ 12,638	$ 5,272	$ 620	$ (5,451)	$ 3,711	$ 7,117	$ 72,060	$ 5,997	$ 26,601
Net (loss) income per basic share attributable to CAI common stockholders	$ 1.86	$ 0.92	$ 0.66	$ 0.28	$ 0.03	$ (0.28)	$ 0.19	$ 0.36	$ 3.74	$ 0.31	$ 1.28
Net (loss) income per diluted share attributable to CAI common stockholders	$ 1.81	$ 0.90	$ 0.65	$ 0.27	$ 0.03	$ (0.28)	$ 0.19	$ 0.36	$ 3.68	$ 0.31	$ 1.27