Summary of Significant Accounting Policies - Basic and Diluted Net Income Per Share Calculations (Details) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2018	Sep. 30, 2017	Sep. 30, 2018	Sep. 30, 2017
Basic net income per share calculation:
Numerator - Net income	$ 93,747,000	$ 64,442,000	$ 264,122,000	$ 147,181,000
Denominator - Weighted average common shares outstanding (in shares)	77,145,023	76,678,584	77,116,377	59,371,202
Basic net income per common share (in dollars per share)	$ 1.22	$ 0.84	$ 3.42	$ 2.48
Diluted net income per share calculation:
Numerator – Net income	$ 93,747,000	$ 64,442,000	$ 264,122,000	$ 147,181,000
Denominator - Weighted average common shares outstanding (in shares)	77,145,023	76,678,584	77,116,377	59,371,202
Dilutive shares contingently issuable (in shares)	345,954	553,514	326,177	539,142
Weighted average diluted common shares outstanding (in shares)	77,490,977	77,232,098	77,442,554	59,910,344
Diluted net income per common share (in dollars per share)	$ 1.21	$ 0.83	$ 3.41	$ 2.46